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2008 TRB Annual Meeting Papers

Traffic Operations and Intelligent Transportation Systems

Traveler Information Delivery Mechanisms: Impacts on Consumer Behavior
- Khattak A., X. Pan, W. Williams, N. Rouphail, and Y. Fan

Advanced traveler information systems or ATIS help individuals make informed decisions regarding activity participation and travel. Presently, ATIS applications use a variety of delivery mechanisms, including the Internet, telephone, television, radio, variable message signs, and in-vehicle navigation devices to support decisions about destinations, travel mode, departure time, routes, parking, and trip cancellation. Over the years, the salience and use of these technologies has evolved. It is now important for both researchers and practitioners to review the status of ATIS technologies and to understand travelers' access and response to their deployment. Focusing on largely public sector delivery mechanisms, this study answers two fundamental questions: Whether or not accessing more information sources is associated with a higher likelihood of travel decision adjustments and which technologies are more likely to elicit substantive adjustments to routine travel? These questions are answered by using a comprehensive and recent behavioral dataset, collected in the Research Triangle area of North Carolina. The study generates knowledge that is potentially helpful in improving existing and future traveler information systems.

Evaluating Traveler Information Impacts on Commercial and Non-Commercial Users
- Pan X. and A. Khattak

Incidents often account for nearly half of traffic congestion in urban areas and add uncertainty to transportation networks. The costs of incident-induced congestion, often in the form of delays, are borne by motorists and commercial carriers and/or associated businesses. In fact a higher burden is borne by commercial carriers, given their higher costs and value of time. Dynamic traveler information about incidents disseminated through electronic media can benefit users. This study explores the extent of benefits associated with dynamic traveler information and whether network delays increase or decline when 1) travelers can observe incidents, 2) commercial truck percentages increase in traffic, 3) truck drivers divert to alternate routes in the same way as motorists do as opposed to lower diversion rates, and 4) when commercial trucks have a higher value of time compared with passenger vehicles. Using a behavioral model, we simulate the movement of commercial trucks and passenger vehicles in a simple transportation network. The results show how dynamic traveler information may (or may not) benefit commercial and non-commercial users, under different scenarios. The implications for incident management are discussed.

Economic Impact of Traffic Incidents on Businesses
- Khattak A., Y. Fan, and C. Teague

Provision of reliable transportation is becoming a key to success for many businesses. By adding uncertainty to travel times, incidents and resulting congestion on Interstate highways impose significant costs on business operations and regional economic development. This paper presents an effort of quantifying the economic impact of traffic incidents on North Carolina's Interstate facilities. Carriers and businesses were carefully selected for interviews and case-study developed based on their substantial shipping needs. Analyses of 29 selected firms are conducted, showing an average hourly cost of unexpected delay of $145 to the surveyed firms. A more focused analysis of case-study interviews by sector and region shows various types of businesses and regions differ in their sensitivity to unexpected congestion. Transportation and warehousing displayed the highest hourly cost among sampled industrial sectors, followed by the retail trade and manufacturing sectors. When expanding interview results to the sampled regions and industry sectors in North Carolina, the Charlotte metropolitan region incurs the highest overall costs and manufacturing incurs the highest overall cost among sampled industrial sectors. Case studies of interviewed businesses/shippers further showed that a majority used information technology to track shipments. However, few sought pre-shipment traffic information or were aware of available traffic information services. The surveyed businesses generally expressed a desire for better communication and information services from the state DOT. It is clear from this study that businesses incur costs due to unexpected delays on the Interstate system, adding to the cost of production. The implications of the results are discussed.

Planning and Traveler Behavior

Associations between environment and mode choice: Does trip purpose matter?
- Shay E., D. Rodriguez, and A. Khattak

Earlier empirical work suggests that travel mode choice is sensitive to both environmental and household measures. This paper uses three different quantitative representations of the physical environment to model mode choice for three trip purposes. We find that mode choice is sensitive to environmental measures; specifically, choice of the walk mode is associated with walkable and accessible environments. Trips differ by purpose, with home-based work trips sensitive to the environment but not socio-demographic variables, but the more discretionary other home-based trips showing the reverse. This suggests that home-based work trips may be more responsive than other trips to strategies aimed at inducing mode-shifting by changing environmental conditions.

Urban form, individual spatial footprints, and travel: Case-study of the Triangle area in North Carolina
- Fan Y. and A. Khattak

An important aspect of addressing current environmental and health challenges involves understanding the connection between urban form and spatial characteristics of individual activity-travel patterns. This paper examines how individuals' spatial activity and travel patterns are related to factors in residential environments including urban form and traffic conditions, after controlling for weather and individual/household characteristics. Behavioral data come from the 2006 Greater Triangle Region Travel Study in North Carolina. Individuals' activity and travel patterns in space are respectively measured by daily activity space-the minimum convex polygon that contains all the daily activity locations, and daily travel distance. We find that densely developed neighborhoods with better connected streets, more retail stores, and more sidewalks generally saw smaller area size of daily activity space and shorter daily travel distance, which indicates the potential of ameliorating transportation problems through land use strategies. Additionally, various dimensions of urban form are compared in terms of their importance in explaining individuals' spatial activity and travel patterns. Sidewalk coverage is found to be a key factor relating to spatial activity and travel patterns.

Household excess travel and neighborhood characteristics: Case of the Triangle area in North Carolina
- Fan Y., A. Khattak, and D. Rodriguez

Excess commuting, the amount of travel not required by the distribution of jobs and houses, has been used to examine commuting efficiency and the relevance of commuting for location choices. This study proposes an alternative estimation approach of excess travel using activity dairies, extending it to non-work travel, and capturing the inter-household variation. The proposed method is demonstrated through a case study of the Triangle Area in North Carolina. The case study shows that Triangle households can achieve an average of 30% reduction in daily travel distance by hypothetically moving to locations that minimize travel. Substantial variation in excess travel is revealed among Triangle households. A regression analysis further investigates whether neighborhood characteristics such as density, diversity, connectivity and walkablity can explain some of the inter-household variation in excess travel after controlling for household attributes. Potential gains in travel efficiency-decreases in excess travel-are found in neighborhoods with higher land use density, retail mix, and street connectivity, suggesting households in such neighborhoods appear to take advantage of the possibility of reducing excess travel when making travel choices. In addition to the negative effect on excess travel, better connected streets in the neighborhood are further associated with decreases in households' minimum required travel distances. The implications of the results are discussed.