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2007 TRB Annual Meeting Papers

What can activity engagement tell us about daily drive time and walking time?
-Yingling Fan and Asad Khattak

Time use is a key aspect of human life and a good understanding can lead to more appropriate transportation and land use policies. While time use issues have been explored extensively from the perspective of activity participation and travel, there is still a need to understand how people allocate time to ignored activities such as walking versus driving. In particular, more walking and less auto use can have a variety of health and environmental benefits. Using daily time use and demographic data from the 2003 American Time Use Survey (ATUS), this work develops an empirical framework to examine the interplay between travel time allocation (walk and drive), activity engagement (what is done, where and with whom), individual/household socio-demographics, and spatial/temporal factors (metropolitan status, weekday/weekend). Tobit models show that walk and drive time allocation respond differently to activity engagement indicators and individual/household/environmental variables in terms of the effect size and direction. Discretionary activity (including leisure, recreation, spiritual and volunteer activities) is a stronger negative predictor of daily drive time, compared to work and shopping activity. Social and family events are associated with less auto use, compared to activities pursued by the individual alone. Living in metropolitan area leads to less daily drive time and more daily walking time. Results imply that compact urban form is associated with reduced auto use.

Autos, Trips and Neighborhood Type: Comparing Environmental Measures
-Elizabeth Shay and Asad Khattak

Understanding the link between the environment and travel may inform policy that has the potential to influence household travel behavior. Transportation planners have long recognized a role for the environment in travel behavior, although techniques for incorporating the built environment in travel research remain under development. This study uses neighborhood type, along with other common household measures, as independent variables in models for auto ownership and travel. Further, we compare three different approaches to incorporating the built environment in modeling and assess their ability to predict auto ownership and use across different types of neighborhoods. Using 1) simple environmental measures, 2) factors (indices) generated by factor analysis, and 3) a neighborhood typology derived from cluster analysis of the factors, we find the factors to provide information the clusters and simple measures do not. Further, we find that auto ownership relates to household variables, while trip generation is more sensitive to built environment factors, as well as household variables and auto ownership.

Wireless Location Technology-based Traffic Monitoring: Preliminary Recommendations to Transportation Agencies Based on a Synthesis of Experience and Simulation Results
-Michael D. Fontaine, Brian L. Smith, Aron Hendricks, and William Scherer

There has been a growing interest in using anonymous tracking of wireless devices as a way to generate travel time and operational data cost-effectively. Unfortunately, there are relatively few independent, quantitative evaluations of these systems. The evaluations that exist are often not widely available, so agencies often enter into deployment agreements with a limited understanding of the abilities and limitations of this technology. This paper provides an overview of the results of past deployments of wireless probe monitoring systems and discusses a simulation effort to gain further insight into the predominant type of system on the market today, handoff-based monitoring systems. Past deployments show that early generation systems that used signal analysis and triangulation encountered significant problems in generating accurate speed estimates. More recent tests using handoff-based technology have shown improvement in data quality at some sites, but there still is not enough data to fully characterize whether those systems can consistently provide useful operational data. The simulation study indicates that the way in which the cellular network topology overlays the roadway network could be a critical determinant of overall system effectiveness. The simulation results indicate that speeds can often be estimated to within 5 mph of reality with handoff-based systems. Based on the synthesis of past deployments, it appears that transportation agencies have often not specified any performance requirements for deployed systems. Agencies may wish to specify minimum performance requirements for data accuracy and availability as a way to ensure that useful information will be generated.

Evaluation of Highway Safety Corridors
-Michael D. Fontaine and Stephen Read

Several state transportation agencies have recently started creating highway safety corridor (HSC) programs in an effort to reduce crashes, injuries, and deaths on roads with a high rate and frequency of crashes. HSC programs use a coordinated campaign of education, enforcement, and low-cost engineering measures to address safety issues. Fines for moving violations are increased in these HSCs as a way to strengthen the potential impact of enforcement. While several states have implemented these programs, little information is publicly available on how these programs have impacted safety. Virginia passed legislation establishing a state HSC program in 2003. This legislation increased fines for moving violations within the HSC, subject to a $200 minimum for criminal infractions and $500 maximum for traffic offenses. This paper documents the initial evaluation of the HSC program on two interstate HSCs. Travel speeds before and after the HSC designation are examined at one site, while crash data are presented at both interstate locations. Public opinions on the HSC program are also discussed. The results of the analysis indicate that little improvement in speed compliance and safety was observed at the congested, urban interstate site. Significant reductions in crash frequency were observed at the more rural interstate location, with a reduction in crash frequency of almost 30 percent being estimated in the most recent year. While results to date have been mixed for the two corridors, the results do show promise. More consistent effects may be possible if more dedicated resources were invested in the program.

Assessing the Benefits of Smart Work Zone Systems
-Michael D. Fontaine and Praveen Edara

Smart work zones (SWZs) are being deployed around the United States as a way to inform drivers dynamically about traffic conditions within a work zone. SWZs use sensors to detect traffic flow conditions on the work zone approaches. These data are then used to alert drivers of congestion or speed differentials in an effort to improve operations or safety. Agencies that are considering deploying SWZs are often faced with the challenge of trying to justify the cost of an SWZ system to decision makers who may be more inclined to use the funds for more traditional maintenance purposes. Although a number of states have evaluated SWZ systems, there has not been much effort to identify trends across multiple tests or extend those findings to predict likely impacts of proposed deployments. This paper synthesizes the results of a number of deployments of SWZ technology and identifies some common trends in performance. The data are then used to develop benefit-to-cost (B/C) ratios for a variety of traffic and diversion alternatives. The B/C ratios are then used to identify some project duration thresholds at which an SWZ would be beneficial based on user delay savings for a two-lane directional segment.

Field Evaluation of Rational Speed Limits
-H. Daniel Son, Michael D. Fontaine, and B. Brian Park

In 2004, speeding-related crashes accounted for over 13,000 fatalities in the United States , and many studies also indicate that speed and/or speed variance are leading causes of crashes on U.S. highways. Thus, it is believed that establishing adequate speed limits, combined with appropriate enforcement and public information and education, can significantly improve the safety of the traveling public by better regulating travel speeds.

This paper presents the results of a field implementation of credible, well-enforced, and highly publicized speed limits on two limited access highways in Virginia where speed limits were increased by 10 mph to 65 mph. The study was conducted over a period of 2 years, and both before and after data on public perception, crash experience, and speed were analyzed. The public perception survey results showed that the new 65 mph speed limits established based on an engineering study were well supported by the public, with over 80 percent agreeing with the new speed limits. The speed data analysis showed that the average speed increased by a statistically significant margin immediately after the new speed limit was implemented, but no practically significant changes were observed during the periods where additional enforcement and education were present. In addition, during the entire study period, the speed variance was fairly consistent, which suggests that crash likelihood was not increased due to the increased posted speed limit. Crash data showed that the enforcement and education campaign was effective at keeping crashes at levels that were not statistically higher than those seen prior to the speed limit change.