Greater Greater Washington

Posts by Ben Ross

Ben Ross was president of the Action Committee for Transit for 15 years. His new book about the politics of urbanism and transit, Dead End: Suburban Sprawl and the Rebirth of American Urbanism, is published by Oxford University Press. 

Complex traffic signals make streets less safe

Streets across the United States are often difficult and dangerous to walk on because wide lanes invite drivers to speed. That isn't all that makes them dangerous, though: many also have signals that distract drivers and draw their eyes away from the road.


Arlington's Intersection of Doom. Drivers who want to turn right in order to travel north from the eastern side of the intersection have to account for oncoming north-bound cars, people crossing from all directions, and confusing signs. Photo by the author.

A case in point is the "intersection of doom" where the Mount Vernon Trail turns into the Custis Trail at the foot of the Key Bridge in Arlington.

Drivers exiting I-66 are allowed to make right turns on red, except during a brief "leading pedestrian interval" when a walk signal gives pedestrians and cyclists a head start across North Lynn Street before the traffic light turns green. But it's hard to see how drivers can make this turn safely without extra eyes on both sides of their head.


Base image from Google Earth.

Drivers must simultaneously watch for cars coming from the left, cyclists and pedestrians entering the crosswalk from the right, and an overhead signal that went in in January that flashes a no-right-turn graphic for a few seconds during the leading pedestrian interval.

To make things worse, the no-right-turn graphic is hard to see in bright light, and it is flanked by highly visible signs that seem to say turns are allowed.

Diligently watching the short-lived no-turn signal while looking for a gap in oncoming traffic from the left would make it nearly impossible to look to the right. A driver trying to legally turn right on red has no time to look toward the sidewalk on their right and can't see whether someone is about to enter the crosswalk and pass in front of their car.


Overhead signs at intersection of doom, with the no-right-turn sign illuminated.
Photo by the author.

Dangers like these are widespread on American streets. What makes this intersection stand out is the heavy bike and pedestrian traffic, not the arrangement of the signals.

Tell drivers what they need to know, and repeat it

From an engineering point of view, the information traffic signals send to drivers is part of a control system that must operate reliably to keep roadways safe. So is the drivers' reaction to that information.

The traffic engineering establishment certainly recognizes that human behavior affects road safety. But two concepts are conspicuously missing from its guidelines on human factors in signal design: redundancy and parsimony.

Redundancy means backups for missed signals and improper actions. Parsimony means signals aren't excessively complex.

It's easy to see redundancy's value. Intersections with simple red-yellow-green traffic signals are full of redundant information: The movement of vehicles and pedestrians is a cue to when the light changes, so drivers don't need to stare at the signal and can keep watch on the street.

More complexity—turn arrows, walk signs, rules that allow right turns on red—means less redundancy. Demands on the driver's eye and brain increase, and the inevitable moments of inattention do more harm.

Parsimony is a less intuitive idea, but an equally important one. This principle, which originated from the statistical analysis of time series, warns against using too many input variables to control decisions. Adding complexity, when there aren't enough data to do it right, makes outcomes worse.

Consider the countdown clocks attached to walk signals. The Federal Highway Administration mandated them when research indicated that when pedestrians know how much time is left before cars start to move, they get hit by drivers less often. But this information changes the behavior of drivers too. Whether the drivers speed up to beat the light or simply get distracted is not clear, but the effect is real. A recent study in Toronto found that countdown timers cause more collisions than they prevent.

Complex signals have other costs. Turn arrows make signal cycles longer. This gets more cars through the intersection, but everyone waits longer for a green light and the street becomes a barrier to walking. The delays to pedestrians and non-rush-hour drivers may exceed the time saved from reduced congestion—but the traffic engineers won't know without data on off-peak travel, something they rarely measure.

And slow lights create safety hazards of their own. The longer pedestrians are asked to stand and watch a don't walk signal, the more likely they are to ignore it.

It will never be possible to govern traffic with the mathematical precision of electric circuits. But they are both control systems afflicted with random noise, and similar principles apply.

Solving problems by adding more gadgets to an already complex system can do more harm than good. Traffic control operates most reliably when everyone on the road knows that green means go and red means stop.

Turn arrows and separate walk signals should be used sparingly. They squeeze more cars through an intersection in rush hour, but they exact a price in safety, dollars, and travel delay.

Traffic engineers need to balance vehicle throughput against the benefits of redundancy and parsimony. In any control system, and especially in one that relies on the actions of human beings, simplicity has to be a priority.

A Maryland road widening will be more costly than the transit it replaces

Maryland governor Larry Hogan wants to build roads with money saved from cancelling the Baltimore Red Line and cutting back the Purple Line. The governor says the two light rail lines cost too much. But his marquee highway project, a wider Route 404 on the Eastern Shore, looks to be far less cost-effective than either.


Route 404. Photo by Doug Kerr on Flickr.

The Route 404 widening will turn 12 miles of two-lane road between Route 50 and Denton into a four-lane divided highway. The work will cost $204 million: $160 million in new money plus $44 million budgeted earlier.

The governor presents his road plan as a way to speed traffic. But the travel time savings from widening Route 404 will be far more expensive than the time saved by the two rail lines.

The two-lane road only backs up on summer weekends when people drive to the beach. According to Google maps, the average traffic delay on summer Friday and Sunday afternoons varies from zero to six minutes. By a generous estimate, this adds up to 60,000 hours lost each year in traffic backups, making the construction cost $3,400 per annual hour saved.

Building the Purple Line will cost $288 per annual hour of rider benefits, and the number for the Red Line is $456. The amount of money the state is spending to save a minute of travel time on Route 404 is seven and a half times greater than the amount it refused to spend to save a minute of travel time in Baltimore. That means a Baltimore bus rider will wait an hour so that an auto passenger can get to the beach eight minutes faster.

Highway safety is another goal, but widening 404 may not help much

Eastern Shore officials offer another rationale for widening Route 404. There are many fatal crashes on the road, and they suggest that the planned widening will fix that. But it's unlikely that the death toll will go down significantly.

Using web searches and a memorial website, I found descriptions of 11 fatal crashes on Route 404 since 2010. Seven of them were on the 12-mile section of two-lane highway; four on the 12-mile stretch that is already four lanes.

Of the seven collisions on the two-lane road, only two involved vehicles crossing the center line. Three vehicles were hit from the side as they turned onto 404 from side roads. There were two rear-end collisions. On a four-lane divided highway, center-line crossing would be impossible, but turns would be more difficult. These numbers suggest that widening 404 would only modestly improve safety, if at all.

Also of note: five of the 11 crashes involved tractor-trailers. Requiring through trucks to use US 50, which has far fewer intersections without signals, might have prevented most or all of these.

Moreover, former Maryland highways chief Parker Williams has said that Route 404 isn't an especially dangerous road, which implies that highway safety money could be better spent in other places. For the cost of widening 404, the state could install some 2,000 of the flashing crosswalk lights known as hawk beacons. They would undoubtedly have saved a good number of the 630 pedestrian lives lost on Maryland highways between 2009 and 2014.

The highway projects in Governor Hogan's package have never gotten the sort of detailed assessment of costs and benefits that the Red and Purple Line projects were subject to. The numbers for Route 404 suggest that cancelling the Red Line was not at all the cost-conscious decision the governor presented it as.

Montgomery won't make (some) businesses fund parking anymore

Builders in downtown Bethesda, Silver Spring, and Wheaton are now free to build as little parking as they want, without violating zoning rules or paying extra taxes. The change eliminates a major subsidy to driving and will help these suburban centers evolve into walkable urban areas.


Photo by BethesdaNow.com Staff on Flickr.

The new policy, enacted as part of the new county budget, is the result of the simpler, more modern zoning code approved a year ago. The rewrite of the zoning ordinance sharply cut the amount of off-street parking required near Metro stations, upsetting a long-established system for financing the county's public parking garages.

When the county first opened public parking lots, they were a way for stores in old downtown buildings to compete with new malls and their ample free parking. Meter rates were low and downtown buildings paid an extra "parking tax" to meet the expenses. Newer buildings with their own parking were exempt from the tax.

After Metro came to Bethesda and Silver Spring, the downtowns grew denser. But for many years the county kept the tax high to encourage the construction of as much parking as possible when new buildings went up. Unless a building met the parking requirement that the zoning code imposed on auto-oriented development far from Metro, it paid the entire tax.

The new zoning code recognized the downside of too much parking, and it lowered the parking minimums near Metro. When it went into effect last year, many buildings that previously paid the parking tax became exempt. This brought confusion at first, and then a recognition that the parking tax had lost much of its revenue-raising potential.

The new county budget solves this problem by setting the parking tax to zero, and making up the difference with other revenue. (The tax has technically not been abolished. If the county fails to pay back money borrowed to build garages, bond holders can demand its resumption.)

At work here is the interconnected nature of land use planning. Automobile-dependent development has a logic in which parking and highways create a need for more of the same. Once that cycle is broken, a new logic sets in. When things work well, as they did here, advances in livability and walkability beget more progress.

Purple Line: It's not the cost, it's the country club

Maryland governor Larry Hogan may cancel the Purple Line because he says it's too expensive, but given his sudden announcement last week of lower highway tolls, that's clearly just an excuse. The real obstacle to building the light rail line is the pressure of a few well-placed opponents, chief among them the Columbia Country Club.


Columbia Country Club in 1919

Back when the Purple Line was a new idea, I had the chance to shake hands with then-governor Parris Glendening. I grabbed the opportunity to say a few words about the project. Glendening's answer? "Get the country club to take two strokes off your score if you hit a trolley car, and you've solved the whole problem."

Almost 20 years have gone by since then, and the situation has not changed.

If the Purple Line dies, cost will be the excuse rather than the real reason. The project's current financing plan calls for only $288 million in state outlays during construction. This is a very modest amount of money for a major transportation facility—the price of two highway interchanges. The savings that Transportation Secretary Pete Rahn has identified will make the number even smaller.

Over the six years of construction, Maryland will spend less on the Purple Line than on last week's toll cuts. The toll cuts, targeted to benefit big trucking companies and owners of beach houses, will cost $54 million a year.


The financing plan for the Purple Line. Image by Ronit Dancis.

Everything else in the light rail construction budget is money that the state loses if it doesn't go ahead. $1.6 billion comes from the federal government, $900 million as a grant and $700 million as a low-interest loan under the TIFIA program. The state has already spent more than $200 million, and Montgomery and Prince George's Counties will kick in at least that much.

The loan, of course, will have to be paid back after the trains start to run. At an interest rate of 2.73%—what Fairfax pays on money it borrowed last December for the Silver Line—the payments will be $36 million a year for 30 years. If the Purple Line's private partner gets $12 million a year in profit and return of capital—a generous return on an initial investment of $81 million—the total will be $48 million. This is still less than the ongoing cost of the toll cut giveaway.

So what would make Governor Larry Hogan, whose slogan is "Maryland is open for business," think of canceling a project that business badly wants? It is certainly not the merits of the arguments against it, which have been thoroughly debunked.

In politics, wealth and influence can be more persuasive than facts and logic. Columbia Country Club, whose golf course lies on both sides of the railroad right of way the Purple Line will follow, has long been a favored haunt of Washington power brokers. The club only reluctantly abandoned its 25-year struggle against light rail in 2013, and after last year's election a team of lobbyists was assembled from its membership to renew the fight.

In January, Governor Hogan came to Bethesda for a fundraiser where club members raised $47,000 for his political committee. Three top members of his staff later sat down with the club's golfer-lobbyists to hear their objections. Neither the governor nor his staff have been willing to meet with Purple Line supporters, and—with a decision just days away—the governor has not even bothered to take a look at the Purple Line's route.

Make no mistake about what is happening. No one here is balancing competing public policy priorities. Either Governor Hogan already understands the Purple Line's vast economic benefits, or he doesn't care enough to find out. The decision he makes next week will be a straight-up choice between insider influence and the public good.

Correction: An earlier version of this post had a typo that said $700 billion as a a low-interest loan under the TIFIA program, rather than $700 million. We've fixed it.

Consumers say they like trains. Why don't economists care?

One of the most basic tenets of standard economics is that consumer choice dictates the market. Yet in discussions about transit, many economic analyses seem to throw consumer preference out the window, insisting that riders' preference for rail over bus doesn't matter, or is imaginary.


Photo by Joshua Daniel Franklin on Flickr.

Opponents of rail projects often argue that trains are a waste of money because buses provide the same benefits for less cost. That's incorrect on technical grounds, but it also ignores the factor of consumer preference.

The great virtue of markets, mainstream economics asserts, is that they compel producers to make what the "sovereign consumer" desires. Each individual buys what he or she wants and isn't forced to accept what someone else thinks they should want.

But as I recently discussed in more detail in Dissent magazine, transportation economists often ignore a basic premise of their own discipline, and dethrone the sovereign consumer.

Be complete and be honest

Unlike their colleagues who study ordinary markets, transportation economists don't try (as they could) to measure consumer preference and weigh the costs of meeting it. Instead, they tell commuters who yearn for trains that their preferences are mere emotion and myth.

Telling consumers they're wrong to feel the way they do is extremely unusual, and transportation economists' insistence upon doing so undermines honest economic assessment of transportation proposals. Most commuters have options, and every freedom to put their preferences to practice.

This is not to say there aren't economic advantages to buses. Of course there are. Buses are generally cheaper, so cities can use buses to run more transit routes to more places than they could on a rail-only system. That's a genuine benefit. It matters, and it's why we'll always have dozens or hundreds of bus routes for every rail route.

So economists are correct to assert that buses can offer great value. But the fact that buses are great on their own terms does not mean consumer preference for rail can be left out of economic analysis.

A trade pact might change local land use decisions in a big way

A key principle of land use in the United States is that homeowners can often veto new buildings on nearby land that other people own. A trade agreement that's currently in the works could have a huge impact on that long-established system of local control.


Hand shake image from Shutterstock.

The Trans Pacific Partnership (TPP) is a trade pact that would change the rules for investments and trade among its signers. It's currently in behind-closed-doors negotiation among 12 countries, including the United States, Australia, Canada, Japan, Mexico, and Singapore. Other countries could join later.

A recently leaked draft of the TPP gives investors from member nations the right to sue when a decision by a local government "interferes with distinct, reasonable investment-backed expectations."

Panels of private lawyers chosen by the investors and the federal government will meet to decide the suits. If the investors win, the federal government must reimburse them for the loss of future profits.

Critics of the TPP argue that it could gut environmental and health regulation. They point to the past history of trade agreements to back up that concern. The TPP's backers, on the other hand, assert that the treaty only bans arbitrary or discriminatory actions.

No matter who turns out to be right about that, the pact is likely to undermine local oversight of land use.

The TPP goes against the spirit of American land use law

Homeowners' power to influence development—what I call "suburban land tenure" in my book Dead Endis an entitlement that most people in the United States take for granted. But it is just the sort of local decision-making the TPP seeks to curb.

Trade treaties aim for decision-making that is stable, predictable, and rational. US land use regulation, on the other hand, bends to meet the often capricious desires of the neighbors. Local officials turn to hard-to-pin-down concepts like "compatibility" and "historic significance" to justify their responsiveness to constituents.

Whatever one thinks of this arrangement, its linguistic evasions are unlikely to satisfy panels of trade lawyers meeting thousands of miles away, under rules that don't even guarantee the local government the right to speak.

Consider this hypothetical case, which is also utterly routine: A foreign landowner proposes a new city building. Neighbors petition for a "historic" designation for the house now standing on the property, and the preservation board approves, blocking new construction. Meanwhile, there are no petitions or designations for nearby houses similar in age and architecture. Is the landowner entitled to compensation?

Or let's say the master plan for an area near a Maryland Metro station calls for 15-story buildings. The zoning allows such tall buildings only if the planning board approves the design; otherwise property owners are limited to three stories. A foreign landowner applies to build a 15-floor building, but neighbors protest against the height of the structures and the planning board cuts the size to nine floors. Will the landowner get the value of the square feet he wasn't allowed to build?

A lot depends on the treaty's details, but we aren't privy to those

It's hard to say exactly how the TPP would affect land use regulation in these and other cases. Wording for the agreement isn't final yet, and that will certainly influence how arbitrators rule in the future. But if Congress gives trade negotiators "fast track" authority, the public will have no say in what follows. Negotiations will stay behind closed doors, and Congress won't be able to change provisions it doesn't like.

Once the pact goes into effect, amendments will require a unanimous agreement from all the countries that signed.

Even after the TPP passes, it will take years for the legal issues to play out. What will happen then if foreign landowners are winning large financial payments from the federal government? Will foreign developers refuse all compromise with local zoning boards, knowing that rejection wins them the same profits as approval? Will the federal government interfere with local zoning decisions that could provoke a large payout? Will domestic builders demand the same rights as foreigners?

You don't have to be a fan of current land use practice to object to this transfer of power. All too often, zoning laws empower affluent minorities at the expense of the larger community. They outlaw the lively urban neighborhoods that more and more Americans want to live in.

The cure for these ills is more democracy, not less. Land use regulators should answer to the entire electorate, not to small groups of influential landowners and not to unaccountable tribunals that put the interests of big money ahead of the common good.

When a safety campaign blames victims it's counterproductive

The region's highway agencies have begun their annual Street Smart campaign promoting road safety. Unfortunately, many of the ads undermine safety by blaming the victim, and advocating the misconception that pedestrians are mere obstacles to cars.


Advertisement that blames the victim. Image from Street Smart.

In this year's version of Street Smart, roadside posters designed for visibility from fast-moving vehicles depict pedestrians as sad-looking young people with car tire tracks across their faces. Although some of the ads do target driver behavior, many wrongly imply that it's pedestrians' responsibility to avoid being run over by inattentive drivers.

Don't blame pedestrians for bad road design

One such sign adorns a bus shelter on Sunnyside Avenue, in Beltsville.


All other photos by Jeff Lemieux unless noted.

Smaller print at the bottom of the sign, which you can only read if you're on foot, adds insult to injury. It advises pedestrians to "Use crosswalks. Wait for the walk signal," the implication being that crosswalks are the only place you can cross the street.

But getting to the nearest traffic light with a crosswalk requires walking an extra 1,500 feet, an unreasonable distance on foot. Instead, bus riders who get off at this location walk across four lanes of traffic to reach businesses on the other side of the road.

Even though there's no marked crosswalk, this is perfectly legal and necessary behavior. Maryland law allows people to cross the street anywhere unless there's a traffic light at both adjacent intersections. Pedestrians have the right of way at intersections and marked crosswalks; drivers elsewhere.


Sunnyside Avenue in Beltsville.

Combine the unsafe street design with the victim-blaming ad and the implied message becomes clear: Pedestrians aren't welcome to use Sunnyside Avenue, and it's their fault if they die trying. The only thing bus riders learn from the ad is that getting to the stop could kill them.

That's not useful public education. It tells drivers not to watch out for pedestrians, and it discourages walking. Heeding these messages will make streets less safe and more congested.


Sunnyside Avenue.

This year's campaign isn't the first time Street Smart has run bizarre ads. Ads in 2011 seemed to suggest pedestrians are a bigger danger to cars than vice versa.

Hopefully future campaigns will avoid this pratfall. It really shouldn't be that difficult.

Whether they live close in or far from the city, people travel about the same number of miles on transit

Transit in the DC area is not just for urbanites. Residents of counties farther from the center of the region ride as many miles per day on transit as those who live closer in.


Daily miles traveled per household. Table from COG report on cycling and walking.

Some drivers and and politicians in exurban counties complain that their counties' gas taxes are paying for urban transit riders. In reality, it's just the opposite: denser areas subsidize the long-distance travel that sprawl requires.

Only a small part of transportation revenue (22% in Maryland) comes from the gas tax. And drivers get most of that back because gasoline is exempt from sales tax. Most money spent on roads comes from taxes on income, real estate, general sales, and automobile sales and registrations. These taxes don't go up if you drive farther.

The above table comes from a new Council of Governments report on cycling and walking. The report used data from the agency's 2007-2008 Household Travel Survey to calculate the daily distance traveled per household by each means of transportation.

By this measure, transit gets the most use not in DC or Arlington but from residents of Prince William County. They ride 6.6 miles per day; Montgomery is second at 6.4. DC clocks in at 5.6 and Arlington and Alexandria, at around 4.5 miles a day, are behind Fairfax and Frederick Counties.

It's not that the region's outer reaches aren't automobile-dependent; residents of exurban counties do 90% of their travel by car. It's that spread-out land use patterns make them travel farther and force them to use cars for most trips.

When destinations are far apart, people take fewer trips on transit. But each trip is longer, on average, and the total distance on transit is about the same as closer in.

The high driving rate in the DC suburbs does not make transit unnecessary. It only proves that the more highways you build, the farther people have to travel to get anywhere. The last thing we should be doing is forcing even longer trips.

The Intercounty Connector's traffic is light so far, but the road's future is still unclear

Planners routinely overestimate how much traffic will grow in the future in order to justify new highways. Usage of the Intercounty Connector is still growing but it looks like the ICC, too, will get less use than planners thought.


ICC traffic levels, in vehicle miles traveled per year. Image by Claire Jaffe.

At first glance, traffic on the ICC seems sparse, and as many journalists report, drivers are taking far fewer trips on the road than predicted. But the trips are longer—about 9½ miles on average, compared to the 6½ miles forecasters expected. Also, the road's initial "ramping up" phase, which is when traffic grows rapidly as drivers learn about a new highway, has not yet ended.

Shifting forecasts

The total miles traveled on a road in a year, which engineers call vehicle miles traveled (VMT), takes into account both the number and length of trips; VMT gives a more accurate measure of traffic density than looking at the number of trips alone. ICC forecasters, like the journalists, focused on trips rather than VMT, but we can tease some VMT approximations out of their reports:

  • In 2004, when the state decided to build the highway, planners foresaw VMT equal to 433 million miles in 2030.
  • A more detailed study in 2006 predicted 325 million VMT in 2020 and 390 million in 2030.
  • In 2009, after construction began, estimates went down further to 278 million in 2020 and 319 million in 2030.
From numbers in the state toll authority's financial statement for the twelve months ending last June, I calculate that VMT in that year was about 195 million. If traffic increases at the rate the forecasters expected (and the just-opened connection to US 1 adds 7% more VMT), it will reach 281 million in 2020 (the upper green line on the graphic above). While that would fall short of pre-construction forecasts, it would at least match the estimate from 2009.

No matter the forecast, the ICC is seeing less usage than planners expected

But it doesn't look like things are headed that way. When they made their models, planners assumed that the overall use of motor vehicles would grow. Data shows that this trend ended about 10 years ago, both in Maryland and elsewhere, and there's not much to say it will start back up. Without long-term increases as part of the projection, the future level of ICC traffic drops to a steady 241 million miles a year (lower green line). That's substantially below all the forecasts.

The range of possible outcomes is even wider than those two numbers suggest. If the initial ramp-up, whose duration is very hard to know beforehand, continues longer than expected and automobile use resumes its historic growth, future traffic might meet the early forecasts.

That, however, is not what's been happening lately. If anything, the ramp-up is coming to an end more quickly than the forecasters predicted. Moreover, if affluent homeowners leave the outer suburbs and new residents who can't afford tolls move in, traffic could peak short of 241 million VMT and then decline.

Even at best, the ICC's tolls will repay only a third of its construction costs. If, as seems probable, traffic on the ICC falls short of the 2009 forecasts, it will need even bigger subsidies. Before Maryland spends more money on toll highways, it should give its projections a second look.

If Maryland kills the Purple Line, it's asking for a $650 million parking bill

If Governor-elect Larry Hogan chooses not to build the Purple Line, he will sock Maryland taxpayers, commuters, and businesses with a huge bill they don't expect. Building parking garages for drivers who would otherwise take the train would likely cost over $600 million, much of it public money.


Bethesda's $64,000-per-space garage under construction. Photo by author.

Parking is expensive, and in the built-up areas where the Purple Line would run, there's no empty land; new spaces would have to go in garages above or below ground.

If there's no Purple Line, more people will leave home in cars, and more parking will be needed at their destinations:

  • Purple Line planners predict that people will take 9,850 new trips on the train that start from their homes. Altogether, they forecast the Purple Line attracting over 29,000 new one-way transit trips each day.
  • With an average of 1.1 passengers per car, canceling the light rail line will create a need for 8,955 additional parking spaces at whatever destination people making home-based trips arrive at.
  • 3,018 of these trips will terminate in downtown Bethesda and Silver Spring, where new parking has to go underground. 4,796 will end elswhere in the inner suburbs, where above-ground garages are the norm.
Montgomery County is now paying $64,000 per space for an underground garage and $53,000 per new space for a parking structure. At these prices, the cost of this destination parking will be $447 million. This does not include parking for people who travel to D.C. or Virginia, or the value of land used for parking lots in outer Maryland suburbs.

Without the Purple Line, downtown residents and students would need more parking space

Cars have to go somewhere at the end of their trips too. The Purple Line won't cut the cost of parking at single-family homes, but apartments and dormitories will need more parking without it.

A rough estimate is that two thirds of the 2,479 new transit riders who live in Bethesda and Silver Spring will live in downtown apartments, and of them, half won't own cars if they don't drive to work. If the Purple Line doesn't go in, new apartment buildings will need more underground spaces, at a cost of $48 million.

Students are not included in the planners' count of home-based trips. University of Maryland administrators expect the Purple Line to greatly improve transit access, and they need to use space currently occupied by parking lots to expand the school itself. As such, they have decided to ban on-campus parking by resident students. The ban will eliminate the need for 2,889 parking spaces, but it's unlikely to go into effect without the Purple Line. If the Purple Line goes, Maryland will need a new parking garage—an expenditure we can estimate at $153 million.

The parking spaces all these drivers will need are going to cost a lot

The cost of all these garages adds up to $648 million. Government funds will pay for parking for University of Maryland employees and students and public garages in Bethesda and Silver Spring. These could add up to as much as half the total.

The remaining cost of the Purple Line for Maryland and its counties, after subtracting federal aid and money already spent, is $1.3 billion. If Maryland shortsightedly cancels this project, the state wouldn't just throw away immense benefits in livability and economic development. It would see half of the supposed cost savings vanish into parking garages.

Clarification: The original version of this post listed 9,850 as a number of trips that start from home on the Purple Line. This is the number of new transit trips (trips that would otherwise be taken by car) that start from home, not the total number of home-based trips on the line.

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