Evaluation of a Travel Time Information System

Transcription

1 Evaluation of a Travel Time Information System Mr Torbjørn Haugen SINTEF Technology and Society, Transport Safety and Informatics, Norway. Adress: NO-7465 Trondheim - Phone: torbjorn.haugen@sintef.no ABSTRACT Over the last years we have developed a system for registration of travel time and other section data with use of ETC tags. The system consists of an infrastructure with 14 antennas and communication lines, and a travel time information system with software, algorithms, website and DMS. Results from other projects has shown that section data constitute a well suited basis for evaluation of traffic flow quality, and is well suited for traffic information and route guidance systems. This paper presents the traffic information system, the test site, the evaluation of the system and the information services available. KEYWORDS Dynamic Traffic Information, Travel Time, ETC-Tags, Evaluation INTRODUCTION Electronic Toll Collection (ETC) systems are common in Norway, both as toll rings in small and large cities, and as toll plazas on road sections. The worlds first ETC toll plaza was opened in 1987, in the city of Ålesund, Norway. The first ETC city toll ring was the Oslo Tolling System opened in The toll systems are now based on automatic detection. Every time a vehicle passes a toll station the station number, passing time and tag identification is recorded. ETC is used for financing of road infrastructure in Norway. ETC technology has also made it possible to widen traffic data registrations to include section data like travel time and delay. This type of data has proved to constitute a well suited basis for evaluation of traffic flow quality, and with that well suited for traffic information and route guidance systems. For travel time purposes we are concerned about the protection of privacy. The travel time information system we have developed is based on national standard AutoPASS ETC-tag. That technology makes it possible to store information within the tag. When a vehicle with this tag passes an antenna the system read information from the tag and writes new information back into the tag. Instead of reading tag identification (and identifying the vehicle), we now can just store timeand-place (TAP) information in the tag at one travel-time measurement point, and read this 1

2 information at the next. Therefore, the travel time is now calculated based on the TAPs stored in the tag, and we consider that problems with protection of privacy are avoided. The travel time system has been evaluated though a Factory Acceptance Test (FAT) and a Site Acceptance Test (SAT). The FAT aimed to test the functionality of the solution. The SAT aimed to verify the correct installation of the system including correct setup and configuration. Both tests are carried out and accepted. THE TRAVEL TIME SYSTEM Norwegian Public Roads Administration has now developed an anonymous travel time option within the new ETC tag system. The system functionality is basically to store time-and-place (TAP) information in the tag at one travel-time measurement point (TTMP), and read this information at the next TTMP, before a new TAP is stored. Based on the TAPs stored in the tag, the travel time can be calculated. System Overview The travel time system can be divided into three parts as shown in figure The travel time information system 2. The network 3. The travel time measurement point (TTMP) Figure 1 The travel time system 2

3 The travel time information system is the part where data is stored and average 5-minutes travel time is calculated. Vehicles that have stopped between two TTM points are sorted out before aggregating the data. The network is a private network not open to the public preferable solved by configuration of the routers only communicating with other known routers, and it is built with fixed lines. The network is used to configure the Multireaders, and to transmit registered data from Multireaders/Tag directly to the TTM server. Timing between the measurement points is crucial and needs synchronization. For this purpose, the server in the TTM system will also be an NTP-server. At the TMMP the Multireader is communicating with the tags (or OBUs = On Board Units) through DRSC link. Every time a vehicle with tag passes a MultiReader travel time data is read and transmitted to the TTM server. The Multireader consists of an antenna, microwave electronics circuitry and a real-time computer. The tag is a 5.8 GHz DSRC Transponder designed for automatic registration of vehicles. System Functionality The system functionality is basically to store time-and-place (TAP) information in the OBU at one travel-time measurement point (TTMP), and read this information at the next TTMP, before a new TAP is stored. Based on the TAPs stored in the OBU, the time of travel may be calculated. The writing of TAPs inside the AutoPASS OBUs must not affect and overwrite the existing logs of normal AutoPASS ETC passings. The normal log for AutoPASS ETC is 100 entries, whereas the number of TAPs stored for the TTMP-application is 4. The new TAP written at a TTMP, will overwrite the oldest entry. Under no circumstances will the OBU-ID be read and stored. Internett, TCC, VMS, DMS, SMS/MMS Dynamic Database Travel-time measurement point 3 Tolling Station Travel-time measurement point 2 Travel-time measurement point 1 Figure 2 Illustration of the test site for ETC tags 3

4 As the vehicle passes TTMP 1: 1. The TTMP will read the TAPs for travel time calculation. 2. The TTMP will overwrite the oldest TAP with a new TAP 3. The TTMP will communicate all 5 TAPs to TTM server for travel-time calculations. As the vehicle passes TTMP 2: 1. The TTMP will read the TAPs for traveltime calculation. 2. The TTMP will overwrite the oldest TAP with a new TAP 3. The TTMP will communicate all 5 TAPs to TTM server for travel-time calculations. As the vehicle passes an AutoPASS tolling station: 1. An ordinary AutoPASS ETC transaction is executed including a new entry to the AutoPASS log 2. The log pointer is incremented. As the vehicle passes TTMP 3: 1. The TTMP will read the TAPs for traveltime calculation. 2. The TTMP will overwrite the oldest TAP with a new TAP 3. The TTMP will communicate all 5 TAPs to TTM server for travel-time calculations. Writing of TAPs inside the tag must not affect and overwrite the existing logs of normal toll station transactions. The normal transaction log in the tag is 100 entries, whereas the suggested number of TAPs stored is 4 (entry ). The new TAP written at a TTM, will overwrite the oldest entry in the TTM log. As long as we just use the TAP s, and not any tag identification, no vehicle is identified. Therefore, we consider the system for anonymous. THE TEST SITE An important part of the travel time system is to test and evaluate the solution in real traffic. Therefore, a test site equipped with 14 Mulitireaders (7 in each direction) is established on a 120 kilometer long section of highway E18 in eastern Norway. The test section goes from Oslo to Larvik through the county of Vestfold, Buskerud and Akershus. This is a road with high traffic density and traffic congestion problems. The test section consists of a 4 and 6 lane freeway from Oslo to Horten (about 75 km) and a 2 lane highway from Horten to Larvik (about 45 km). We have only one Multireader in each direction, even on multilane freeways. The Multireader is usually placed above the right lane. Table 1 Location of Multireaders in southbound direction Location Distance between Multireaders [km] Road section Lysaker / Oslo Lierskogen lane freeway Drammensbrua North lane freeway Drammen South lane freeway Kopstad lane freeway Tønsberg lane highway Larvik lane highway 4

5 Table 2 Location of Multireaders in northbound direction Location Distance between Multireaders [km] Road section Larvik Tønsberg lane highway Kopstad lane highway Drammen South lane freeway Drammen North lane freeway Asker lane freeway Lysaker / Oslo lane freeway Figure 3 Picture from the location Drammensbrua North The proportion of vehicles with OBU varies over the test section. Near Oslo the proportion is very high (about 90%), and in the south near Larvik the proportion is down to about 60%. This is still more than enough for travel time purposes. EVALUATION The travel time system has been evaluated through a Factory Acceptance Test (FAT) and a Site Acceptance Test (SAT). The FAT aimed to test the functionality of the solution. The SAT aimed to verify the correct installation of the system including correct setup and configuration. This test also focused on data quality and the amount of colleted data compared to the number of vehicles with tags. Both tests are carried out and accepted. 5

6 Factory Acceptance Test (FAT) The testing is divided in two parts: A laboratory test performed at Q-Free A test at Rotvoll toll station with cars running through a gantry with Multireaders The laboratory tests consist of: 1. Rotor test 2. AutoPASS log integrity test 3. DynamIT transaction structure 4. Software stability measure The test at Rotvoll toll station consists of: 1. Live AutoPASS The functionality of the solution is tested and accepted. Especially the interaction between the Multireader and the ETC-tag was tested with both TTMP and AutoPASS ETC configuration. Site Acceptance Test (SAT) The SAT consists of at field trial where travel times was measured both automatically with use of tags and manually with use of video registrations and license plate recognition. The field trial was carried out on two sections: Kopstad Tønsberg (Southbound direction) Drammens Sør Drammensbrua Nord (Northbound direction) Videocameras were installed at the same locations as the Multireaders, i.e. in both ends of each section. Recording was taken over a period of one hour. Licence plate numbers was read from the videotapes. A special software tool (ATLAS ) developed at SINTEF were used to match vehicles and calculate travel times. Only vehicles with tags were used. Figure 4 show the proportion of vehicles with tag at the downstream Multireader, and the proportion of matched vehicles at the two sections during the one hour period of the field trial. The blue bars are the proportion of tagged vehicles. The red bars show the proportion that has passed both the upstream and the downstream Multireader on the section. This is the vehicles that produce the travel times on the section. 6

7 Proportion of Vehicles with Tags Proportion Vehicles with Tag at the downstream Multireader Proportion of Vehicles with Tag that are mached 70.0 Proportion [%] Kopstad - Tønsberg Section Drammen Sør - Drammensbrua Nord Figure 4 Proportion of tagged vehicles on the two sections at the field trial. Number of Registrations on the Section "Kopstad - Tønsberg" Tags vs Manual Registrations Number of Vehicles Tags Manual :10 09:15 09:20 09:25 09:30 09:35 09:40 09:45 09:50 09:55 10:00 10:05 10:10 Time of Day Figure 5 Number of matched vehicles with tags and manual registrations When comparing the number of travel times (matched vehicles) from tags and video we found that tags generally provided more registrations. There could be several explanations to this result: 1. Usually the tag is placed on the middle and the top of the windshield. However, some vehicles has coloured/dark windshield that makes it difficult to determine whether they have tag or not. Other vehicles can have the tag just lying loose on the dashboard, and it could be difficult to see on the video recording. 7

8 2. On both sections there are 2 lanes in one end, and 1 lane in the other end. The Multireader is only mounted over the right lane even if there are two lanes in the same direction. Some tagged vehicles in the left lane might be read by the Multireader. We have to do some more detailed analyses to determine this, and we plan to have these results ready to the ITS World Congress. Figure 5 show the number of travel times from tags (automatic registrations) and video (manual registrations) in each 5 minutes time interval on the section between Tønsberg and Kopstad in southbound direction. The blue bars are the number of travel times from tagged vehicles, and the red bars show the results form the manual registrations. The tendency is the same on the other section, Drammen Sør Darmmensbrua Nord, in northbound direction. The tag has more matched vehicles than what we found from the manual registrations with videocamera/atlas. The travel times are measured in a period with low traffic, which means only small variation in travel time from vehicle to vehicle and from time interval to time interval. The average travel time in each 5 minute interval is approximately the same when comparing data from tags and manual registrations. All in all the results are satisfying, and they verify a correct installation, setup and configuration of the tag system. The only mystery that remains to solve is the small difference in the number of matched vehicles from tags and manual registrations. Other Field Data On some locations we also have loop detectors close to the Multireader. Two sections are selected for closer evaluation of tag proportion over the week. The two sections are: Drammens Sør Drammensbrua Nord (Northbound direction) Asker Lysaker (Northbound direction) The fist section is a short one, and the undelayed travel time is approximately 6 minutes. The section has a high proportion of vehicles with tag passing both upstream and downstream Multireader (Figure 7). Traffic problems usually occur in the weekends when the proportion of recreation traffic is high. Figure 6 shows average travel time and traffic volume on a Saturday and a Sunday in June On Sunday evening the travel time increase considerably. This is also the time with the lowest proportion of tagged vehicles. However the proportion is never below 6%, which is more than acceptable for travel time calculation. 8

9 Section : Drammen Sør - Drammensbrua Nord Travel Time and Traffic Volume 00: : : Travel Time [tt:mm] 00:30 00:25 00:20 00: Traffic Volume [Veh/h] Travel Time Traffic Volume 00: : :00 0 Time of Day Figure 6 Travel Time and Traffic Volume on the Section Drammen Sør Drammesbrua Nord one weekend in June 2005 Section : Drammen Sør - Drammensbrua Nord Proportion of "matched" Vehicles with Tag Proportion of Tags [%] Time of Day Figure 7 Proportion of matched vehicles with tags on the Section Drammen Sør Drammesbrua Nord one weekend in June 2005 The second section (Asker Lysaker) is longer, and it has several junctions between the two Multireaders. Undelayed travel time is approximately 9 minutes. This section has a typical morning peak and afternoon peak. High traffic volume, unstable traffic flow and increased travel time occurs every day. In periods with unstable traffic flow we get the typical drop in traffic flow. 9

10 Section : Asker - Lysaker Travel Time and Traffic Volume 00: : : Travel Time [tt:mm] 00:30 00:25 00:20 00: Traffic Volume [veh/h] Travel Time Volume both lanes Volume right lane 00: : :00 0 Time of Day Figure 8 Travel Time and Traffic Volume on the Section Asker Lysaker two weekdays in June 2005 Section : Asker - Lysaker Proportion of "matched" Vehicles with Tag Right Lane Proportion of Tags [%] Time of Day Figure 9 Proportion of tagged on the Section Asker Lysaker two weekdays in June Figure 8 show that during nighttime almost all the vehicles use the right lane. So having just one Multireader the right lane is the best placement. The proportion of vehicles with tag passing both upstream and downstream Multireader is lower than on the other section, but still we get reliable travel times. Lowest proportion occurs in the morning peak. 10

11 Algorithm The algorithm that select vehicles (individual travel time) for calculation of average travel time is also under continuous evaluation. We have tried to simplify earlier algorithms, and this seems to work well under most traffic conditions. We have done some adjustments in time periods with few (only 1 of 2) tagged vehicles. If only one vehicle has passed both upstream and downstream Multireader within the last 5 minutes, we have to compare this with the average travel time in earlier intervals, to verify whether the travel time is correct or not. TRAFFIC INFORMATION SYSTEM The main purpose of the travel time registrations is to inform travellers about the current traffic situation between Oslo and Larvik. Information will be provided through: 1. The Internet 2. Media 3. VMS / DMS Internet Solution Average travel time and delay (for both directions) are presented in real time as text and numbers. The data are updated every 5 minutes. Delay is presented on a stylistic map by using four colour codes for symbolizing four different traffic situations. The colour codes are: Red: Heavy delay Yellow: Some delay Green: No delay Grey: No data available Figure 10 Internet Solution 11

12 Media An important target group who could spread information to travellers on the road is radio stations. Several channels have special programs with traffic information, and the internet page is one of their information sources. Dynamic Message Sign and Route Guidance Along the road information is given to drivers through variable message signs / dynamic message signs informing about the traffic conditions. So far all the signs are located in the southern part of the test section (Larvik-Drammen). On this part of the section we have a route guidance system showing drivers alternative routes. Figure 11 show one of the message signs controlled from the Traffic Control Centre. The message on the sign says: Delay to Oslo 20 minutes Decreasing Figure 11 DMS with information about delay When a message is displayed, information about alternative routes is given as well. During normal traffic conditions all signs are blank. 12

13 CONCLUDIG REMARKS Anonymous and reliable travel time registrations are something that we have been seeking for several years. System evaluations confirm functionality of the solution, the quality of data, correct setup and configuration. The number of travel-time measurement points will expand in the future. Not only for real time travel information systems, but also for monitoring and documentation of the traffic conditions REFERENCES [1] Eriksen, T., Giæver T. and Haugen, T. (1995). Traffic Control and Information towards the Year of Final Report. SFT63 A SINTEF Civil and Environmental Engineering, Transport Engineering. Norway. [2] Haugen T. (1996). The Section Data Project. Analysis of Point and Section Data. SFT22 A SINTEF Civil and Environmental Engineering, Transport Engineering. Norway. [3] Haugen T. (1997). Traffic Information on E18. Evaluation of the VMS signs. SFT22 A SINTEF Civil and Environmental Engineering, Transport Engineering. Norway. [4] Haugen T. and Giæver T. (1998). Improving Traveler Information and Route Guidance by Use of Automated Vehicle Recognition. In proceedings 5 th Wold Congress on ITS. Seoul, Korea. [5] Q-Free (2003): System specification for travel-time measurement system using MD5850 and MD5885. Q-Free document number Norway. [6] Wold H. (2003). Traffic Information on E18 in Vestfold. [7] Wahl R., Flø M., Haugen T., Bang B. and Lillestøl P. (2003). Dynamic Transport Information - State of the art. SFT22 A SINTEF Civil and Environmental Engineering, Roads and Transport. Norway. [8] Haugen T. and Wold H. (2004). Travel time registration using etc tags in Norway. In proceedings from 11 th Wold Congress on ITS. Nagoya, Japan. [9] Q-Free (2004). FAT Report for DynamIT. Q-Free document number Norway. [10] Wahl R., Haugen T. and Lillestøl P. (2004). Dynamic information services within the transport sector The DynamIT project. In proceedings from 11 th Wold Congress on ITS. Nagoya, Japan. 13