Michael Mauch

Freeway Traffic Oscillations: Observations and Predictions

Freeway traffic was observed over multiple days and was found to display certain regular features. Oscillations arose only in queues; they had periods of several minutes; and their amplitudes stabilized as they propagated upstream. They propagated at a nearly constant speed of about 22 to 24 kilometers per hour, independent of the location within the queues and the flow measured there; this was observed for a number of locations and for queued flows ranging from about 2,000 to 850 vehicles per hour per lane. The effects of the oscillations were not felt downstream of the bottleneck. Thus, the only effect on upstream traffic was that a queues tail meandered over time by small amounts. (For the long queues studied here, the tails deviated by no more than about 16 vehicle spacings, as compared with predictions that ignored the oscillations). Notably, the character of queued traffic at fixed locations did not change with time, despite the oscillations; i.e., traffic did not decay. There were changes over space, however. New oscillations formed in moderately dense queues near ramp interchanges and then grew to their full amplitudes while propagating upstream, even though the range of wave speeds was narrow. The formations of these new oscillations are strongly correlated with vehicle lane changing. But this pattern of formation and growth was less evident in a very dense queue (caused by an incident), although frequent lane changing occurred near the interchanges. It thus appears that the oscillations were triggered by random lane changing in moderately dense queues more than by car-following effects. Finally, kinematic wave theory was found to describe the propagation of the oscillations to within small errors. For distances approaching one kilometer, and for 2-hour periods, the theory predicted the locations of vehicles to within about 5 vehicle spacings. Further analysis showed that some of these small discrepancies are explained by differences in car-following behavior across drivers.

AN OBSERVED TRAFFIC PATTERN IN LONG FREEWAY QUEUES

A simple exercise in data analysis showed that, in queued traffic, a well-defined relation exists between the flow on a homogeneous freeway segment and the segments vehicle accumulation. The exercise consisted of constructing cumulative vehicle arrival curves to measure the flows and densities on multiple segments of a queued freeway. At this particular site, each interchange enveloped by the queue exhibited a higher on-ramp flow than off-ramp flow and as a consequence, motorists encountered a steady improvement in traffic conditions (e.g., reduced densities and increased speeds) as they traveled from the tail of the queue to the bottleneck. This finding has practical implications for freeway traffic planning and management. Perhaps most notably, it suggests that the first-order hydrodynamic theory of traffic is adequate for describing some of the more relevant features of queue evolution. This and other practical issues are discussed in some detail.

Gender, Race, and Travel Behavior: Analysis of Household-Serving Travel and Commuting in San Francisco Bay Area

Detailed trip diary data from a 1990 survey of San Francisco Bay Area residents were used to examine the effects of race/ethnicity on the differences in commuting and household-serving travel among men and women. With respect to travel behavioral differences between men and women, the findings suggest that women do more child chauffeuring and make more household-serving trips than men. This analysis further reveals that these gender differences in commuting behavior extend to household-serving travel and can vary significantly by race/ethnicity in addition to income and household structure. It was found, for example, that commute time differences are highest among whites (4.5 min) and lowest among Hispanics (1.8 min), whereas observed gender differences in average travel time for all trips do not vary much by race or ethnicity. Furthermore, the gender variation in child-serving trips was lowest among Asians and Pacific Islanders (women are 60 percent more likely to make such trips) and highest among whites (women are 223 percent more likely to make such trips). Finally, and in contrast to child-serving travel, women make about 75 percent more grocery trips than men, regardless of race/ethnicity. The analysis suggests, however, that much, although not all, of the racial/ethnic variation in the travel behavior of men and women is probably explained by factors—such as income, employment status, metropolitan location, and automobile availability—that tend to vary systematically by race ethnicity. In general, it was found that gender is a far more robust predictor of child-serving and grocery shopping trips than either race or ethnicity.

Meeting SB1 Transportation SystemsPerformance Goals

Author(s): Mauch, Michael; McKeever, Benjamin; Skabardonis, Alexander | Abstract: This research project directly addresses the Caltrans policy question of “How to meet the SB 1 ten-year (2027) mandated preliminary performance outcomes for additional state highway investments?” More specifically, the study focuses on performance outcome number 4: “Not less than 90 percent of the transportation management system units in good condition”. As part of this project, the research team evaluated the Caltrans performance-based methodology to achieve the 90% performance goal in addition to completing a review of relevant reports from the Federal Highway Administration (FHWA), state departments of transportation, and Caltrans. The research team also conducted multiple meetings, phone calls and emails with Caltrans management. The research team found that the Caltrans Transportation Asset Management Plan, which governs its SB 1 implementation, follows FHWA guidance and published best asset management practices. Further, Caltrans has a solid asset management plan in place to meet the SB 1 target. The research team also provides several recommendations including but not limited to: 1) Caltrans should continue working on defining deterioration rates or models for transportation management systems (TMS), 2) state of being in “good condition” for TMS must be more clearly defined, 3) Caltrans should continue monitoring innovations in asset management, and 4) Caltrans should consider conducting more pilots of performance-based ITS maintenance.

California’s Freeway Service Patrol Program: Management Information Systems Annual Report Fiscal Year 2015-2106

The Freeway Service Patrol (FSP) is an incident management program implemented by Caltrans, the California Highway Patrol and local partner agencies to quickly detect and assist disabled vehicles and reduce non-recurring congestion along the freeway during peak commute hours. The first FSP program was piloted in Los Angeles, and was later expanded to other regions by state legislation in 1991. As of June 2012, there were fourteen participating FSP Programs operating in California, deploying over 350 tow trucks and covering over 1,750 (center-line) miles of congested California freeways. The purpose of this research project was to evaluate the effectiveness of the Caltrans FSP program in reducing incident durations and removal of other obstructions that directly contribute to freeway congestion for Caltrans fiscal year 2011-2012. The project provides valuable information to agencies managing the FSP program so that resources are distributed within the various statewide FSP operations in the most efficient and cost-effective manner possible. The tools used and the operational performance measures provided by this research effort will significantly contribute on the ongoing agencies’ efforts to improve the efficiency and effectiveness of the FSP program.