True Average Speed Measurement
Availability: Now
True Average Speed may be used in a variety of applications
Houston Radar DR500S, DR500C and DR1500 radars feature a 'True Average Speed' calculation and output. Existing radars in the field may be updated to support this feature via a simple firmware update. The radar internally calculates and periodically updates a vehicle count weighted average traffic speed on the road over a user-determined time period taking into account all incoming lanes of traffic and speeds of all vehicles.
Additionally, it also accumulates real-time traffic volume binned by speed in 1mph or 1kph bin widths.
This feature provides sub-mph/kph accurate speed information as the vehicle speeds are measured by a direct Doppler shift rather than inferred indirectly. Additionally, setup and deployment are extremely easy, with the radar simply pointed up-stream into traffic without any accurate sighting or extensive field setup requirements.
In many situations where lane-by-lane traffic counts and occupancy are not required this provides a great alternative to side-firing radars at significantly lower price points (<5x the cost), power usage (<20x the power usage) and ease of setup.
Our customers are successfully using this feature for "Slow traffic ahead" and "Travel time to destination" applications.
True Average Speed features
- Calculates 'Real Time' vehicle count weighted average speed on the road in mph or kph
- Excellent average speed accuracy due to direct speed measurement. Typically better than 1mph or kph.
- Fractional speed output availalble.
- Average speed updated on user specified intervals from 5 seconds to 60 minutes.
- 'Real Time' vehicle counts by speed histogram available in user specified bin-widths as fine as 1mph/kph
- No-hassle installation. Simply point upstream. No calibration required on the road.
- Very low cost. Included as part of our In-Radar Advanced traffic statistics feature.
- Retrieve speed remotely via external cellular modem. Native TCP/IP (Internet) network connectivity in supplied Windows host program.
Frequently Asked Questions (FAQ's) About True Average Speed
Q. What is the difference between simple Doppler speed output available from any Doppler radar and 'True Average Speed' in Houston Radar?
A. The Doppler speed available from a Doppler radar is simply a speed value of a single highest speed target or target with the strongest return signal. This speed will vary widely as vehicles are detected and their speed measured.
In True Average Speed mode, our radars internally track individual targets on the road simultaneously, accumulate vehicle counts over a user specified time period (e.g. 30 seconds) and then update the average speed taking into account all the traffic on the road. This gives a much more accurate picture of the traffic pattern on the road.
Q. Are there strict mounting requirements to use this feature?
A. No. Simply mount the radar at least 6 to 15 feet above or away from the road, pointing up-stream into traffic and it will track and measure the vehicle speeds on all incoming lanes. We recommend that you use this feature to monitor no more than 3 lanes of incoming traffic.
Q. How accurate is the speed measurement?
A. Since the speed is measured via the Doppler shift, the accuracy is significantly better than 1mph or 1kph. Additionally, the radar is able to "know" when a vehicle passes it and takes into account the cosine error generated just as the vehicle is passing the radar automatically mitigating the error introduced due to the cosine effect.
Q. Is the True Average Speed available even if I require the raw Doppler speed (e.g. for local traffic calming display purposes)?
A. Yes. You may chose to output the raw Doppler speeds over one serial port and poll for real-time histograms or the True Average Speed value over the second serial port using our binary protocol and thus have access to both features simultaneously. Please note, that the Advanced In-radar traffic statistics option must be purchased for the True Average Speed calculation to be enabled.
Q. Can the radar output lane-by-lane average speed or occupancy data?
A. No. The radar will provide a True Average Speed for all incoming lanes of traffic. It cannot distinguish between individual incoming lanes. Note that the radar will reject all outgoing traffic in the speed and count calculation.
Q. Can I simply average the raw Doppler speed over the serial port and achieve the same result? What's special about 'True Average Speed' done inside the radar?
A. While you can certainly average the raw Doppler speed output from any Doppler radar, you will not achieve the same result. The in-radar True Average Speed is not calculated by averaging the raw Doppler speeds internally, rather by actually counting individual vehicles and then generating a count weighted average speed.
Thus, the simple average calculation performed outside the radar will miss a slow lane of traffic as the radar may prefer the faster lane and send its speed out. The True Average Speed calculation will count individual vehicles in all visible lanes taking into account different vehicle speeds thus giving a much more accurate picture of the traffic on the road.
Additionally, the simple average speed calculation will bias the result towards speeds associated with vehicles picked over a longer distance/time since more updates will be included from these vehicles whereas the True Average Speed actually counts individual vehicles and the range or time of the pickup does not influence the result.
Finally, the internal counting algorithm is able to reject to a high degree spurious pickups (e.g. swaying tree branches, snow flakes, rainfall etc.), whereas all these spurious pickups will be included in the simple average result.