Walkability, parking, and TDM influence whether you drive

Arlington has tried to reduce traffic by clustering development around transit and using transportation demand management (TDM) programs to raise awareness of alternatives to driving. According to a new study of residential buildings, it’s working.

We found that regardless of age or whether a building is condo or rental, people who live in Metro corridors or in areas with high Walk Score indeed take transit more and drive less than the average resident.

Residents were also less likely to drive when their workplaces used TDM programs to inform people about alternatives to get to work. The price of parking also had a strong effect.

Transit use is higher while driving is lower in study buildings

For the study, Arlington County researchers counted cars entering and leaving parking lots at 16 residential buildings which have Transportation Demand Management (TDM) programs. Researchers also counted how full each building’s lot or garage was at one point in time, surveyed residents about their habits, and talked to property managers to get information on each building.

34% of the residents in the study use transit, more than Arlington overall, which has a rate of 27%, and significantly more than the regional average of 21%. Study residents’ commutes are similar to those of commuters who live nearby, but study residents ride transit slightly more.

Access to transit service at home and the walkability of a residential area both result in low rates of driving to work alone. Parking is a powerful factor in how people decide how to get to work, but the availability and price of parking at work is more important than parking at home. And where people work is a strong influence on how they get to work.

Study residents use transit, walk, or bike for 39% of their non-work trips, which is also higher than rates for their immediate neighborhoods. Transit access seems to have a less significant influence on how people travel outside of work, which is clearly related to the extent of services within walking distance. It’s difficult to define the role of residential parking on non-work trips; most likely, it influences vehicle ownership, which in turn influences mode choice.

Whether a building was located within or outside a Metro corridor was the most significant factor affecting trip generation. Outside of Metro corridors, the density of destinations (measured by Walk Score), higher neighborhood intensity, and the availability of a shuttle or free transit seemed to result in fewer car trips. But there was no noticeable difference in the trip generation of apartments and condominiums, or by average age of residents in the building.

We also compared the number of daily and rush hour car trips for study buildings near Metro with the predicted number of car trips from the Institute of Transportation Engineers, and found that they were much lower. ITE also overestimated some trip generation rates for buildings away from Metro as well.

Vehicle ownership, parking influences travel habits

We also looked at how vehicle ownership affected travel habits. Vehicle ownership increased with average household income, and condominium owners owned more vehicles per adult than apartment residents.

There was a definite inverse relationship between vehicle ownership and transit access. Ownership rates were lower in more walkable areas than in “car dependent” areas, but were about the same if the area was “somewhat,” “very,” or “extremely” walkable, according to Walk Score.

Vehicle ownership is strongly related to the cost of residential parking, particularly at a cost of $95 or more per month. But parking occupancy and vehicle use seemed unrelated to the spaces per resident provided.

Overall, parking occupancy within Metrorail corridors was similar for all weekdays. Weekend occupancy was higher, but Sunday evening occupancy was similar to the occupancy on weekday evenings.

TDM makes a difference at work, but not at home

We also found that Arlington’s TDM programs have an impact on how residents get around. 75% of the study respondents had TDM services at work, while 85% of respondents mentioned having at least one home-based TDM service. 56% of respondents had used them before. Awareness of Arlington TDM services was the same as for the County overall, but only 34% of Arlington residents had used a TDM service.

Study respondents who knew of Arlington services took transit, biked, and walked at higher rates for commute and non-work trips than did respondents who were not aware of Arlington services. Respondents who had used TDM services had even higher use rates.

There was a strong relationship between the awareness or use of TDM services in the workplace and use of transit, walking, or biking for commuting. But having TDM services in your building had a more modest relationship to commute mode. Instead, living in transit, pedestrian, or bike-accessible areas seemed to have a greater influence on how respondents got around.

Our analysis shows that people will change their travel habits if the right amenities are present: if their homes and jobs are close to transit; if they live in walkable, bikeable neighborhoods with lots of shops and services nearby; and if they’re made aware of different transportation options.

For more details, see the summary slide presentation, the full slideshow of topline results, the full report, and data tables.

A version of this post appeared at Mobility Lab.