Lane Control with Active Traffic Management for Congestion Reduction-Part of the Series on ‘Lessons from the 2nd International Symposium in Freeway and Tollway Operations’ Conference in Hawaii

article top

The 2nd International symposium in Freeway and Tollway Operations was held in Honolulu, Hawaii from June 21-24, 2009. More than 200 experts specializing in freeway and tollway operations gathered from around the world to share their research knowledge and experiences. These series of articles summarize some of the major presentations with useful lessons for Hawaii. This is article 9 of 10.

Traffic congestion is a major problem in cities with population over 500,000. Congestion levels are not the same day to day even on the same segment of the same highway. This is because the variety of traffic influencing events is never the same. Because of this unreliability, travelers must budget extra time for their trips. There are means however to improve travel time reliability.


Active Traffic Management (ATM) is an important option for improving traffic flow by reducing congestion on highways. Dr. Beverly Kuhn, from the Texas Transportation Institute, made a strong presentation about the potential of improving mobility and travel time reliability by using ATM strategies to reduce congestion on highways. ATM can maximize safety and traffic flow by dynamically managing and controlling traffic based on prevailing conditions. Many different applications of ATM are currently applied on different US highways. Some of these applications are speed harmonization, queue warning, junction control, dynamic re-routing, traveler information, and plus lanes.

Speed harmonization, queue warning, and dynamic re-routing all utilize dynamic message signs to provide information to drivers. Speed harmonization uses them to maintain vehicle flow and reduce the risk of collisions by changing speed limits while approaching congested areas, collisions or special events.

Queue warning utilizes dynamic message signs to provide information to motorists about slow traffic and queues ahead and direct traffic to alternate lanes. The technique makes effective utilization of the available roadway and reduces the likelihood of speed differences and collisions related to queuing.

Traveler information uses dynamic message signs, the internet, radio, GPS devices and sometimes cell phones to provide drivers with route information, travel times, network speeds, and other prevailing traffic conditions along highways. This information allows drivers to make better decisions about the times and routes that they travel.

ATM technologies have been successfully implemented in the US. Some examples are the SR-91 Express lanes located in Orange County, California, the I-10 Katy Tollway located in Houston, Texas and SR-167 High Occupancy Toll (HOT) lanes located in Seattle, Washington.

SR-91 was the first fully automated toll road in the world. Dynamic tolling has been employed and the prices of tolls vary with the prevailing level of congestion on the road. Variable message signs are used to inform travelers about the route details based on the prevailing traffic condition along the highway in each direction. This information helps travelers to know more about incidents, roadwork zones, and speed limits on a specific segment of the highway. In addition, carpools with three or more occupants, motorcycles, zero emission vehicles and vehicles with disabled persons can travel for free, with the exception of evening peak, in the peak direction, when HOVs are charged with 50% of the posted tolls. The 10 mile long express way carriers more than 40,000 people each day and generate revenue (e.g., $39.6 M in 2005).

The I-10 Katy Tollway is a unique example of tollway/managed lanes. It has two lanes in each direction. The lanes primarily serve for mass transit and HOV needs during peak hours (5 to 11 AM, and 2 to 8 PM) in both directions. Carpoolers, vanpoolers and motorcyclists are allowed to use the lanes at no charge during HOV hours. If any unused capacity is available then single occupancy vehicles (SOV) can pay a toll to use the lanes.

The lanes function as a regular tollway during off-peak periods. Similar to SR-91, tolls are collected electronically and are subject to change based on the prevailing traffic condition on roads. The main purpose of dynamic pricing is to maintain an optimum traffic flow. Thus, the operation mechanism of the lanes has focused on efficient utilization of the available facility rather than colleting the revenue.

The existing underutilized high occupancy vehicle (HOV) lanes of SR-167 were converted to HOT to maximize the efficiency of the lane. SOVs can use the high occupancy lanes for a toll when extra capacity is available. The rate of tolls is dynamic based on prevailing traffic conditions.

Most lane management and ATM strategies are not used in Hawaii. Hawaii has many available options to increase its use of ATM. Increasing the use of dynamic message signs for speed harmonization, queue warning or traveler information could all provide drivers with useful information and help manage traffic networks. These technologies have been tried, tested, and found to be valuable elsewhere.

‘Laxman KC is candidate for the Master’s degree in Civil Engineering at the University of Hawaii at Manoa.’