1. What is the Bellevue Real-Time Traffic Map?
The Bellevue Real-Time Traffic Map provides up to the minute real-time traffic congestion information to traveling public. By knowing the current traffic conditions, motorists can make informed decisions on trip planning and route selection, leading to reduced roadway congestion and travel delays for motorists.
2. What is the map telling me?
The map is telling you the amount of congestion present when you approach a signalized intersection in Bellevue. Congestion is measured in terms of how many green lights it will typically take a vehicle to make it through the signalized intersection, and how much backup approaching the signal you are likely to see. For instance, Green (light traffic) indicates little or no backups and that you will quickly make it through the intersection once the light turns green, whereas Black (severe traffic) indicates long backups and that you will typically have to wait two or more green lights to actually make it through the intersection. See question #3 below for more information on map colors. You may also zoom in on the map to look at an area in details. As you zoom in, you will notice color arrows pointing in the direction of the intersection for which the congestion is being measured.
3. What do the display colors mean?
The colors displayed for each roadway segment indicate the amount of traffic congestion approaching the intersection. Green indicates light traffic, with little delays approaching the intersection. Traffic queues are short and once the traffic signal turns green, you will quickly make it through the intersection. Yellow indicates moderate traffic, with some queuing and delays. Once the traffic signal turns green, you will usually make it through the intersection. Red indicates heavy traffic, with significant queuing and delays. Once the traffic signal turns green, you will often have to wait for the next green light before making it through the intersection. Black indicates severe traffic, with long backups and delays. You will typically have to wait for two or more green lights before making it through the intersection. Black could result from very heavy traffic, an accident, construction activity, or some other special events.
4. How did you pick the color codes displayed on the map?
We follow the color scheme used by the WSDOT Freeway Flow Map. The only difference is that we use gray for no data and white for no equipment.
5. Why do some intersections show a left turn or right turn arrow?
Typically, the display color represents the congestion level for all the traffic (left, thru and right) approaching the intersection in that direction. In a few locations with heavy turning volumes, we also indicate the congestion level for those turning movements. You may need to zoom in the display to see the arrows.
6. How does the map work?
Traffic data is collected at Bellevue’s signalized intersections, and sent to the city’s central traffic computer via field communication facilities. The data is then processed and forwarded to the city’s GIS server for mapping and display on the city web site.
7. How is the data collected and processed?
Data is collected from devices called loop detectors that are buried in the pavement on each approach to a signalized intersection. These loop detectors are located about 100 feet back from the intersection. We collect data that measures the percentage of time that a vehicle is located over the loop detector. This measurement is called “occupancy”. We then use the occupancy value and information on the number of lanes to estimate the congestion level on the roadway segment approaching the signalized intersection. For purposes of the map, a roadway segment is the segment of roadway between two the nearest signalized intersections.
8. How often is the data gathered and updated from an intersection?
Data from each intersection is gathered and updated once per signal cycle. Depending on the length of a cycle and the traffic demand, it varies between 25 to 180 seconds. However, the data is saved and sent to the GIS server once every minute.
9. How often is the map updated to display the congestion level?
The flow map refreshes once a minute to display the congestion level.
10. Why are some of the intersections without data?
The roadway section will display no data when we have an equipment malfunction, data communication problem, data maintenance, power outage, or damaged loop detector.
11. Why are some of the streets not included on the real-time traffic map?
The map includes only city arterials that have signalized intersections. Some roadway segments are displayed as white for no equipment. The map is generated from data collected by equipment at the traffic signal (see question #7 above), thus signal equipment is needed to display a road segment on the map. Some common reasons are we do not have a communication link between the signal and the Traffic Management Center at City Hall, or we do not have loop detectors installed. If the distance between two signalized intersections is long, a portion of the segment is also shown as white (no equipment).
12. What are the differences between no data and no equipment?
No data indicates that we normally are able to display a color code for the roadway segment, but at the time we are not getting data back for that roadway segment, typically because of the reasons shown in question #10 above. We will try to troubleshoot and restore the display. No equipment indicates that we do not have the equipment in place to enable us to display the congestion level for that roadway segment. This is typically because of the reason listed in question #11 above. We will be installing additional communication links or detectors as opportunities arise.
13. How accurate is the real-time traffic map information?
Engineers do their best to relate the traffic data collected at each intersection to a level of traffic congestion and color display on the map. In general, we have found through calibration efforts that the map is both reasonably accurate and consistent. Higher precision can be achieved over time through ongoing calibrations, field observation, user feedback and fine-tuning. Users should keep in mind, however, that these are estimates of congestion. Also, the rate of change of congestion is not displayed, and in some instances, could affect the map user. For instance, black could be displayed on a segment although the traffic or accident that resulted in black may be clearing rapidly. The map will inform the motorist of the black condition, but would not be able to inform the motorist that traffic is clearing and the segment may change to yellow shortly. Lastly, the vehicle detection loops described in question #7 may occasionally malfunction. When this occurs, black is displayed because the occupancy value is approaching 100%. Such “false blacks” are not common on the map, but can happen from time to time. Generally, “false blacks” will not occur on more than one adjacent roadway segment, so if you see two or more adjoining red/black segments on the map, this is a very good indication of serious traffic congestion.
14. When should I consider an alternate route?
This will depend upon a number of factors, including trip origin and destination, durations of congestion as well as personal preferences. If you see yellow/green segments and isolated red segment along your trip route, this is an indication that congestion is not present or at least manageable. If you see a series of red/black segments along your trip route, this is an indication of heavy traffic, construction, or some sort of incident. You may consider an alternate route or delaying your trip. If you are able to check the display regularly before your trip, you may able to determine if the congestion is getting better or getting worse.
15. Can I get a traffic camera snapshot directly from the real-time traffic map?
This feature is not available at this time. However, you can get traffic pictures by selecting the link “Traffic Cameras in Bellevue” at the bottom right corner of the map.
16. How does the map help engineers to manage traffic?
The real-time traffic map allows traffic engineers to more readily monitor traffic conditions and identify congestion due to heavy traffic, accidents, construction, or other special events. This in turn will allow engineers to make even better use of the city’s traffic computer network that allows real-time signal timing adjustments at city intersections. Engineers will use the city’s recently expanded traffic camera system to help verify and assess traffic congestion identified on the map. The map will also allow traffic engineers to more quickly identify incidents and signal detection equipment malfunctions.
17. What public benefits does the map provide?
By knowing current traffic conditions, the public can make informed decisions on trip planning and route selection, leading to reduced roadway congestion and travel delays for motorists.
18. What additional features would you like to add to the map?
Possible future map upgrades include:
19. What other cities provide similar traffic maps?
At this time, Bellevue is the first and only city in Washington to provide a real time arterial street traffic conditions map to the public. In fact, there are only a few cities in the US or worldwide to have this kind of GIS based display.
20. Some of the interesting statistics (as of March 2006):
21. Whom should I contact if I have other questions or suggestions?
Send us an email at trafficmanagement@ci.bellevue.wa.us