Handling The Demand

Jan. 1, 2006

Most state highways in the U.S. were built during the 1960s and ‘70s with an infrastructure investment of more than $1 trillion. Many have now exceeded their 20-year design lives and are seriously deteriorated. The consequences are high maintenance and road-user costs because of degraded road surfaces and construction work-zone delays.

Most state highways in the U.S. were built during the 1960s and ‘70s with an infrastructure investment of more than $1 trillion. Many have now exceeded their 20-year design lives and are seriously deteriorated. The consequences are high maintenance and road-user costs because of degraded road surfaces and construction work-zone delays.

The California Department of Transportation (Caltrans), which oversees an 80,000 lane-km system, launched the long-life pavement rehabilitation strategies (LLPRS) program to rebuild approximately 2,800 lane-km of the state’s most severely distressed urban freeways.

Transportation agencies are raising their awareness of the seriousness of traffic delays caused by urban freeway rehabilitation and are experimenting with the use of intelligent transportation systems (ITS) to control traffic demand in construction work zones.

The automated work-zone information system (AWIS) has been on urban freeway construction projects to reduce traffic demand through work zones by providing real-time travel information to road users.

The Federal Highway Administration (FHWA) has been documenting case studies regarding the use of ITS in work zones to raise awareness of these technologies among transportation agencies, highway construction practitioners and the general public. Many state agencies, including Arizona, Illinois and California, have implemented and evaluated AWIS performance.

However, previous case studies have mainly focused on increasing safety within work-zone corridors by taking traffic volume into account and exploring ways to control incidents. Little focus has been placed on the potential of automated systems to lower the volume of traffic during peak hours through the work zone by encouraging diversion to alternative routes within the freeway network.

Rebuilding roadbeds

The I-15 Devore corridor consists of three or four lanes for each direction and carries approximately 110,000 average daily traffic, about 10% of which is heavy trucks. It has uniquely high commuter peaks on weekdays as well as high traffic volume on weekends because recreational motorists travel between Los Angeles and Las Vegas through this corridor.

The I-15 Devore reconstruction project occupied a 4.5-km stretch of the roadway south of the I-15/I-215 junction, roughly 20 km north of the I-15/I-10 junction near San Bernardino in southern California.

In October 2004, a 9 lane-km stretch of badly deteriorated concrete truck lanes was reconstructed with 150 mm of new asphalt concrete base and new 290-mm-thick concrete slabs. Under high traffic volumes, two truck lanes in one direction were rebuilt in 210 hours (about nine days) using a traffic scheme that rebuilt one roadbed while counter flowing traffic on the opposing roadbed. The same project would have taken 10 months using traditional nighttime closures.

While one roadbed was completely closed for the duration of construction activities, the other roadbed was operated with five lanes including one temporary shoulder lane that carried traffic in both directions, accommodated by the use of quick-change moveable barriers.

The counter-flow traffic-control system enabled the provision of three lanes in the peak direction and two in the nonpeak direction during each peak period, with minimal traffic interruption. The barrier was shifted twice a day in less than 30 minutes on a 5-km stretch to provide the dynamic lane configuration.

According to the preliminary traffic analysis performed using the Highway Capacity Manual demand-capacity model, a nominal 10% that was believed to be the most realistic goal achievable in this network geometry traffic-demand reduction during weekday peak hours (6 a.m. to 10 a.m. and 3 p.m. to 7 p.m.) through the work zone would still produce maximum traffic delays of as much as 90 minutes.

The analysis indicated that achieving 20% reduction in peak-hour traffic demand could reduce delays to 45 minutes. To achieve a 20% traffic-demand reduction, Caltrans implemented a public outreach program utilizing the Internet to encourage more road-user “no-shows,” travel pattern changes (mode and trip time) and diversions to detours. Accompanying the public outreach effort, AWIS was introduced onsite and offsite, via the Internet, to provide travelers with estimated travel times through the work zone.

Estimating travel times

The I-15 Devore AWIS consisted of three major components: a remote traffic microwave sensor (RTMS) to collect speed and occupancy of vehicles, portable changeable message signs to display travel-time information and the software on the server to estimate travel time.

These components were connected to each other via a wireless communication system. Three RTMSs for the I-15 northbound direction and two for the southbound direction were located at 1.6-km intervals along the work zone. Additionally, one RTMS was located on I-10 eastbound to monitor traffic conditions along the main detour. Three portable changeable message signs were installed for I-15 northbound traffic and one portable changeable message sign was installed for southbound traffic to enable the travelers to change their routes before entering the work zone.

The software, Virtual Transportation Operations Center, on the AWIS server computer enables the operators to monitor, analyze and integrate traffic data. It was mainly operated on the vendor’s server in St. Paul, Minn., and secondarily monitored by traffic engineers at the Caltrans traffic management center (TMC).

The engineers in the Caltrans TMC had access to override the message on the portable message signs when they found obvious discrepancies between the AWIS travel-time estimates and the actual travel times reported by the probe vehicles. The traffic data (count, speed, classification and occupancy) were collected at the RTMS locations and transmitted to the server station for the travel-time estimation. The estimated travel times at the server were transmitted in real-time to both of the portable changeable message signs onsite and the project website that was offsite. The traffic information messages were classified into three categories based on the severity of traffic delays through the work zone.

The AWIS estimated travel time (ETT) was displayed on the portable and permanent message signs at 10-minute intervals. When the ETT was over 50 minutes (Category 3), the algorithm crosschecked the traffic condition on I-10 eastbound to decide whether or not the detour guidance message should be activated. If the traffic on I-10 eastbound was in a free-flowing condition, all the portable and permanent message signs sequentially displayed the ETT and detour guidance messages with two frames (“TRAVEL TIME 50 MIN FROM I-15/I-210 TO SR-138” and “DETOUR TO I-10 EAST”). When I-10 eastbound was congested, only the ETT was displayed without the detour guidance message.

Outreach on the Internet

The I-15 project website provided the public with construction progress and closure schedule information. The website recorded over 100,000 page visits between August and December 2004. The website updated the estimated real-time travel information from the AWIS so that travelers could be made aware of work-zone traffic conditions before departing on their trips.

The website also provided traffic speeds and snapshot images of the freeway on the traffic roadmap. By clicking a sign on the website roadmap, the AWIS estimated travel time was displayed in text format in real-time. Video streaming features over eight digital camera positions along the I-15 corridor were in service. Eight camera positions provided images at five-second intervals from upstream to downstream through the I-15 work-zone corridor, and travelers intuitively recognized the queue starting point and assumed travel times based on their travel experiences.

The ability to use the project website to access information on traffic conditions through the work-zone corridor prior to their travel departures provided flexibility for motorists in considering travel plan alternatives. Travelers had the options of canceling unnecessary trips or adjusting their departure times or changing travel modes or routes by using public transit or carpool.

In addition to the real-time traffic information provided by the AWIS, the project website posted survey questionnaires to evaluate road users’ travel-pattern changes and public perceptions regarding the AWIS operation and accelerated rehabilitation techniques. Based on the surveys with approximately 400 respondents, the majority (72%) of users found the project information on the website useful for their trip planning.

The effect of reconstruction closures on traffic was acceptable according to a traffic measurement study and web surveys indicating travelers’ traffic delay experiences, such as the following: 27% reported delays longer than 60 minutes, 20% reported delays less than 45 minutes and 53% reported delays less than 30 minutes.

As the actual travel times experienced were closely matched with the estimated travel-time information from the AWIS, survey respondents gave a positive evaluation of the accuracy of the travel-time estimates provided by the AWIS. Twenty-four percent of the survey respondents experienced the travel-time estimates as accurate all the time and 67% commented that the AWIS was accurate at least part of the time.

As a result of AWIS and public outreach, a 20% reduction in traffic demand through the work zone was achieved by the combination of no-shows, diversions and travel-mode changes, thereby reducing the maximum peak-hour delay by 50% (45 minutes instead of the expected 90 minutes). It produced a $3.6 million benefit in potential road-user cost savings. I-10 eastbound was used as the I-15 northbound detour and showed 10% daily traffic volume increase with a peak of 36% in the morning peak hours. I-215 southbound was used as the I-15 southbound detour and showed about 15% daily volume increase.

Fast-track feedback

About 400 respondents to two web surveys on the project website showed a dramatic change in perception of the fast-track construction strategies, swinging from strong initial objection to support for future fast-track projects. Most survey respondents showed initially strong reluctance to the extended closures: 64% expressed an initial preference for the traditional nighttime or weekend closures and 14% even requested to cancel the project.

However, public perception was substantially changed due to the extensive public outreach efforts, including the implementation of AWIS. Of the respondents to the post-construction survey, 70% expressed support for rapid rehab projects. This result indicates that the public is willing to bear the inconvenience of long traffic delays through a work zone for a short period of time if doing so can significantly shorten the overall time a construction project requires.

State highway agencies and decision makers can use the ideas and findings of this case study to efficiently configure and operate AWIS in combination with a public outreach program for heavy-traffic urban highway rehabilitation, with the goal of minimizing public inconvenience.

The I-15 Devore Research Team has been honored with two Caltrans 2005 Excellence in Transportation Awards, one for innovation and another for public awareness. The team also received the 2005 Tranny Award for highway projects issued by the California Transportation Foundation.

About The Author: Lee is a research engineer at the Institute of Transportation Studies, University of California at Berkeley. He can be contacted at 510/665-3637, or [email protected]. Thomas is an operation manager for Parsons Brinckerhoff Quade & Douglas Inc. He can be

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