Smart Work Zone Systems
by
Prahlad D. Pant, Ph.D.
PDP Associates Inc.
2367 Springdale Road
Cincinnati, OH 45231
Ph: 513-226-6009
Fax: 513-851-1019
E-mail: Pant@PDPassociates.com
1.0 Introduction
A freeway construction work zone generally creates conflicts between vehicular traffic and work activity. Work zones not only lead to traffic conditions that violate motorists' expectations but also expose construction workers hazardously close to the fast moving vehicles. The closure of one or more lanes of a freeway section causes a bottleneck on the freeway and reduces the capacity in the work zone. Such a work zone situation is a challenge to one of the main objectives of a traffic management system - the safeand efficientmovement of traffic. In the case of congestion that leads to queuing up of vehicles for several miles of the freeway, the motorists are generally not aware of what is going on ahead of them and how long it will take them to clear the work zone. This is because the information on changeable message signs (CMSs) that are posted along the freeway do not provide real-time information on the expected travel time, delay or speed. Typical displays include "Construction Ahead - Expect Delays" or "Possible Delay Ahead" - but for how long and why, nobody knows. Such messages do not provide specific, accurate and reliable information about the construction and, more often than not, they end up being ignored by motorists. The lack of real-timeinformation is one of the major causes of motorist frustrations in work zones, wherein neither can they plan trips successfully nor adjust their trips based on the information provided. In general, once the motorists get trapped in a traffic jam on the freeway, they are left with no information as to the extent of the jam, its cause, and for how long they are going to be trapped on the freeway. Despite the possible existence of alternate routes, if no definite travel time or delay information is available, drivers are generally hesitant to take such alternate routes as in most cases they are not familiar with the adjacent routes.
A major problem in freeway work zones is the safety of motorists and workers. If motorists are not provided with real-time information, they don't know what delay, speed or travel time can be expected on the freeway. They are caught by surprise when vehicles ahead of them suddenly begin to brake, which often leads to rear-end accidents. Vehicles stray into the work area injuring construction workers. The result is a higher than normal crash rates in freeway work zones.
There exists a necessity to provide accurate and reliable real-time information to motorists as to how long it will take them to clear the work zone, how long they will be delayed by the lane closure, or what speed they can expect ahead of them. This information needs to be provided at reasonable intervals in advance of the work zone as well as through the work zone. The immediate benefit of this kind of information is that it would help the motorists decide whether to stay on the freeway or to take an alternate route since they are now aware of the expected delay due to the work zone.
2.0 Characteristics of Smart work Zone Systems
In recent years, the above-mentioned concerns and necessities have led to the development of smart work zone systems that are designed to predict travel time, delay or speed on a freeway work zone, on a real-time basis. These systems are intended to better inform motorists, encourage them to take alternate routes, reduce their frustrations, reduce freeway congestion, and enhance safety for motorists and workers. These systems can be used to provide real-time information to motorists during incidents, temporary closures, or any unexpected conditions on the freeway.
A "smart work zone system" is the application of computers, communications, and sensor technology to freeway transportation and would possess the following general characteristics:
- Real-time: The system obtains and analyzes traffic flow data in real-time, providing frequently updated information to motorists.
- Portable: The system is portable, hence allowing its installation (with minor modifications as necessary) at different locations.
- Automated: The system operates in an automated manner with as minimal supervision as possible by human operators.
- Reliable: The system provides accurate and reliable information, keeping in mind the serious consequences of misinforming motorists in work zone situations.
These systems, if properly designed and implemented, will:
- Better inform motorists and reduce their frustrations;
- Encourage motorists to take alternate routes;
- Reduce congestion and allow more freely flowing traffic;
- Clear incidents more quickly, thereby reducing secondary incidents;
- Make work zones safer for highway workers and motorists.
In recent years, several companies have developed and implemented smart work zone systems in different states. These companies and their systems are listed in Table 1. A review of these systems is outside the scope of this paper. More systems are expected to be offered by the private sector in the future.
In the following sections, we offer two examples of smart work zone systems called
- TIPS (Traffic Information & Prediction System) and
- ASIS (Advance Speed Information System).
These systems can be used in urban as well as rural freeways. A brief description of these systems is provided below
Table 1.
| Company Name | Name of System |
|---|---|
| PDP Associates Inc. | (i) TIPS (Traffic Information and Prediction System) and (ii) ASIS (Advance Speed Information System) |
| ASTI Transportation Systems | CHIPS (Computerized Highway Information System) |
| ADDCO | Smart Zone |
| National Intelligent Traffic Systems | ITSWorkzone |
| Scientex Corporation | ADAPTIR (Automated Data Acquisition and Processing of Traffic Information in Real-time) |
| United Rentals | AIMS (Automated Information Management System) |
(Note: The above list is provided for information only. The author is not familiar with the working or suitability of any system except TIPS and ASIS. For more information, the reader may contact individual companies)
3.0 Traffic Information & Prediction System (TIPS)
The Traffic Information & Prediction System (TIPS) is a portable, real-time, automated, accurate and reliable system for predicting and displaying travel time for motorists in advance of and through work zones. It collects real-time traffic flow data using roadside non-contact sensors, processes the data in an on-site personal computer, calculates estimated travel times between different points on the freeway, and displays travel time information on portable, electronic changeable message signs positioned at pre-determined locations along the freeway. TIPS can be used as an efficient incident management tool for providing real-time information about accidents, emergency highway closures etc. to the motorists. The system has been designed to incorporate features that make the system adaptable to different work zones. TIPS allows motorists to make decisions about staying on the freeway or taking an alternate route, based on the information displayed on the changeable message signs.
The major components of TIPS are as follows:
- Microwave radar sensors for vehicle detections on each lane of the freeway;
- Microcontrollers for processing the traffic flow data;
- Radios for transmitting traffic flow data to the on-site personal computer (PC), and from the PC to portable changeable message signs;
- Mobile trailers with solar panels and batteries for providing electric power to field equipment;
- Changeable message signs with radios for displaying travel time information to motorists;
- Intelligent traffic algorithm and travel-time estimation models residing in the specially-developed TIPS software in Windows 2000 environment.
Other features of TIPS include:
- a website for providing real-time information to motorists, and
- video cameras for bringing live traffic pictures to the project office and displaying in the website.
The Base Station, consisting of a Personal Computer with the TIPS software and a radio, polls each sensor at 30-sec intervals and receives traffic flow data for each lane. It calculates travel times between different points on the freeway and sends instructions to changeable message signs to display specific real-time travel time messages. The changeable message signs display the messages and send confirmations to the Base Station. TIPS operates in a fully automated mode with minimal human supervision.
TIPS is equipped with a telephone dial-up feature that allows full control of the system from any remote location (office, home etc.). This particular feature is useful for incident management, which allows public agencies to display customized messages on the changeable message signs when necessary. For example, in the case of an emergency when motorists need to be informed of an accident, or when a freeway needs to be completely closed, project officials can remotely transmit special messages to one or more signs from any place.
A few examples of messages displayed by TIPS are shown below. Although TIPS has been shown to display travel times in these examples, the system is equally capable of displaying real-time delay or speed as necessary.
The signs below read: '40 MIN TO END OF WORKZONE', 'WORKZONE ENDS 15 MILES', '44 MIN TO END OF WORKZONE', 'WORKZONE ENDS 19 MILES', 'ACCIDENT AHEAD', and 'HIGHWAY CLOSED AHEAD'.
TIPS was successfully deployed in the following work zones during the past two years:
(1) Deployment in 2000:
- I-75 Dayton, Ohio
- Urban (Downtown)
- Work zone - 3 miles
- Advance area - 11 miles
(2) Deployments in 2001
- I-75 Dayton, Ohio
- Urban (Downtown)
- Work zone - 3 miles
- Advance area - 11 miles
(3) Deployment in 2001
- I-94 Milwaukee, Wisconsin
- Semi-rural
- Work Zone - 12 miles
- Advance area - 7 miles
Independent Evaluation of TIPS in Dayton, Ohio
When TIPS was deployed on a 14-mile segment of northbound Interstate 75 in Dayton, Ohio during the Summer and Fall of 2000, the Ohio Department of Transportation (ODOT) hired Dr. Helmut Zwahlen, Russ Professor Emeritus at Ohio University, to conduct an independent evaluation of TIPS. The results of the study (Final Report, March 2001) are summarized in the following abstract.
"A real-time travel time prediction system (TIPS) was evaluated in a construction work zone. TIPS includes changeable message signs (CMSs) displaying the travel time and distance to the end of the work zone to motorists. The travel times displayed by these CMSs are computed by an intelligent traffic algorithm and travel-time estimation model of the TIPS software, which takes input from microwave radar sensors that detect the vehicle traffic on each lane of the freeway. Besides the CMSs and the radar sensors, the TIPS system includes the computer and microcontroller computing the travel times, 220 MHz radios for transmitting data from the sensors to the computer and from the computer to the CMSs, and trailers with solar panels and batteries to power the radar sensors, CMSs, and radios. The evaluation included an accuracy analysis between the predicted and actual recorded travel times and a survey of the motoring public. Three crews driving independently of each other in the traffic stream recorded predicted and actual travel times at three CMSs to the end of the work zone for 12 hours each day for three consecutive days, resulting in 119 trial runs. The data recorder in each crew also recorded the license plate numbers of private non-commercial vehicles with Ohio license plates. A total of 3177 different license plate numbers were recorded and a questionnaire was sent to each one. A total of 660 completed surveys were returned and analyzed. Based on the regression analysis of actual times vs. predicted times, the system does on the average a reasonable job in predicting the travel times to the end of the work zone. About 88% of the actual times recorded for each sign, and for all the signs combined, were within a range of ± 4 minutes of the predicted time. However, a few differences (actual - predicted) as great as 18 minutes were observed. Survey responses indicated that the motoring public does perceive a certain inaccuracy in the travel times. However, almost 97 % of surveyed motorists felt that a system to provide real-time travel information in advance of work zones is either outright helpful or maybe helpful. In summary we may conclude that the real-time TIPS system represents a definite improvement over any static non-real-time display system. It provides in general and most of the time useful and relatively accurate travel time predictions to the motoring public and appears to be perceived by the motoring public as helpful and useful."
Two specific results of TIPS evaluation in Dayton, Ohio will be presented below:
(1) The study revealed that the time differences for all three changeable message signs combined were as shown in the following table.
Table 2. Time Difference Data for All Three CMSs Combined
| Minutes Off | Frequency | Percentage | Cumulative Percentage |
|---|---|---|---|
| 0 | 49 | 14% | 14% |
| 1 | 117 | 33% | 47% |
| 2 | 75 | 21% | 68% |
| 3 | 51 | 14% | 82% |
| 4 | 20 | 6% | 88% |
| 5-8 | 17 | 5% | 93% |
| >8 | 26 | 7% | 100% |
| Total | 355 | 100% | 
|
(2) In reply to the question "Do you think that such a travel time prediction system in advance of work zones and in advance of exits in heavily traveled freeways where drivers could select an alternate route in situations where long travel times to the end of the work zone are predicted is helpful to the motoring public?", the motorists responded as follows:
Pie Chart Results-Motorists responded with:
Yes, helpful (565) 85%
No, not helpful (17) 3%
Maybe (73) 11%
No response, (5) 1%
Independent Evaluation of TIPS in Milwaukee, Wisconsin
TIPS was deployed on Interstate 94 in Milwaukee, Wisconsin during the construction season of 2001 and evaluated for five States (Iowa, Kansas, Missouri, Nebraska and Wisconsin) that comprise the Midwest Smart Work Zone Deployment Initiative. The evaluation was performed by the University of Wisconsin-Milwaukee and Marquette University. The results of the evaluation were not available at the time of writing this paper. However, a preliminary report of the diversion studies performed by Professor Alan Horowitz of University of Wisconsin-Milwaukee and provided to the author by the Wisconsin Department of Department has concluded that "the before and after analysis supports the notion that TIPS is influencing drivers to change their routes". During this deployment, TIPS provided the motorists with information on real-time travel time to the end of the work zone but did not provide any information as to the availability of alternative routes. The advance area of I-94 had three lanes, which was reduced to two lanes in the work zone. The work zone had a two-lane frontage road that had stop-controlled intersections usually spaced about one mile apart. The road itself jogged at a few places, perhaps giving the impression that it was discontinuous. On Sunday afternoons, which carried the heaviest hourly traffic volumes during the months of July and August, the traffic volume on I-94 averaged to 3144 vehicles per hour between 2 pm and 6:45pm. The before and after analysis showed that 10.0 percent of I-94 drivers chose an alternative route.
Summary of Lessons Learned from Ohio and Wisconsin Deployments
The Ohio and Wisconsin deployments have shown that TIPS is a reliable work zone system that provides:
- Accurate travel time information;
- Is overwhelmingly liked by motorists;
- Influences drivers to change their routes;
- Is an efficient tool for incident management; and
- Can be successfully deployed on both urban and rural freeways.
When the final report of the independent evaluation of TIPS in Milwaukee becomes available in the coming months, it is expected to provide further insights on the accuracy, reliability, and impacts of the system.
4.0 Advance Speed Information System
The Advance Speed Information System (ASIS) is a portable, real-time, automated system that calculates vehicular speeds at downstream segments of a freeway and displays the speed information on changeable message signs at upstream locations. By providing accurate speed information in advance, ASIS assists motorists to adjust their speed according to the most current traffic conditions and reduces the element of "surprise" that often leads to rear-end crashes.
An "ASIS sign" is a changeable message sign that has a microwave radar sensor, microcontroller, radio, modem, and antenna mounted on it and integrated as one device. The system works in the following way: Two or more ASIS signs are placed in series at previously-determined locations along the freeway including (a) advance areas where traffic backups are likely to occur and (b) the work zone itself where conditions can change quite frequently due to the changing needs of construction operations. The sensor picks up signals from each vehicle on each lane, the on-board computer calculates current speed at 30-sec intervals, and the radio/modem transmits speed information to an upstream sign, which is displayed to the motorists in an appropriate format. Examples of messages include:
The signs below read: 'SLOW DOWN', 'SPEED AHEAD 30 MPH', 'PREPARE TO STOP', 'SPEED AHEAD 10 MPH', 'PREPARE TO STOP', and 'STOPPED TRAFFIC AHEAD ', 'NEXT ONE MILE' and 'SPEED AHEAD 25 MPH'.
At least two signs are needed for the operation of this system. Any number of signs can be added as necessary. ASIS signs operate as stand-alone devices and no central control from a Base Station is required for their operation. The system runs 24 hours/day, seven days/week in automated mode.
Optionally, ASIS can be provided with a Base Station that centralizes the operation of the whole system. The Base Station allows project officials to transmit customized messages to any or all signs for incident management. For examples of these messages please refer to the previous photos in the TIPS section.
ASIS is a flexible system that can be tailored to meet the needs of any freeway. ASIS is expected to reduce rear-end crashes and enhance the safety of motorists and workers. Although ASIS was first developed for work zones, it can be deployed on any freeway that experiences recurring or non-recurring congestion.
(For more information on TIPS or ASIS, please visit the website www.PDPassociates.com.)
5.0 Conclusions
Smart work zone systems are designed to improve the safety of highway workers and traveling public, the efficiency of incident management, and the reliability of highway traffic operations while minimizing congestions delays. As evidenced by the independent evaluations of TIPS previously-described in this paper, a smart work zone can provide reliable and accurate information, which can be used by motorists for making decisions. With selection of proper systems and their applications, transportation agencies can provide valuable service to traveling motorists and construction workers in work zones.
