Estimation of Effects of Washington State’s Trip-Reduction Program on Traffic Volumes and Delays: Central Puget Sound Region

Abstract

Washington State requires large employers in its nine most populous counties to encourage their employees to reduce commuting vehicle trips and to monitor progress by surveying employees. The monitoring requirement yields roughly 250,000 surveys every 2 years. Analysis of the survey results for 1999 and previous years estimated that the program removed an average of 18,500 vehicles from the road during the morning peak in 1999, with 12,600 of these in the Seattle metropolitan area. Information from the surveys was used to construct an origin-destination table for these trips, and the table was then used in a four-step modeling process to estimate the corridors and links that realized the greatest effect of the trip-reduction program. The modeling compared a baseline, which assumed effects of the trip-reduction program, with a case in which trips removed were added back into the trip tables. Results indicate that the trip-reduction program has measurable effects on traffic volumes and delay, both areawide and in specific corridors. The analysis is unique in having these types of data on which to draw for a metropolitan area whose modeling system can use them.

Travel plans: a way forward?

“…In the UK, the Department for Transport (DfT, 2005) reports the results of 24 case studies of workplace travel plans carried out in 2004 that indicated reduced car use of between 10% and 25%, while the range for school travel plans is 8-15% and 7-15% in urban areas for personalised travel planning. Next, Hillsman et al (2001) Yet, while clearly attractive, in practice the travel plan has remained a marginal transport planning tool (Boot et al, 2007;Enoch and Zhang, 2008). The question is, why?…”

Travel plans from the developer perspective

“…At the site level Cairns et al (2008) report that 24 workplace travel plans, also known as site-based 'transportation demand management' in the USA or 'company mobility management' in Europe, cut car use by between 10 and 25%, while Hillsman et al (2001) found an average 6% reduction at sites in Washington State, and NTA (2010) reported an 18% reduction in car use from workplace travel plans based on data from Ireland. Meanwhile, the Northamptonshire Transport Strategy for Growth in the UK (NCC, 2007) noted that a combination of good land-use planning and a good travel plan could achieve a modal shift of up to 20% at residential developments.…”