|Type: Field operational test|
|Countries: The Netherlands||? test users|
|? partners||? vehicles|
|Active from 2009 to 2010|
|Rijkswaterstaat, Centre for Transport and Navigation|
|Data catalogue||Tools catalogue|
|Data sets used in this FOT:
No data set is
|The following tools|
were used in this FOT:
No tool is linked
An alternative to fixed speed limits is dynamic speed limits. With variable speed limits, we mean a temporary speed limit, which differs from the permanent speed limit and is set depending on current traffic and environmental conditions. The aim is to improve road safety and traffic flow and to minimize the environmental impact or to improve user acceptance. Also combinations of these goals can be pursued.
In order to gain more knowledge about dynamic speed limits, the project "Dynamax" was carried out. On the highways A1, A12 and A58 Field Operational Tests (FOTs) with various dynamic speed limit applications were carried out. The effects on traffic flow, air quality and noise levels were investigated. Also the effects on driver behaviour and driver acceptance for dynamic speed limits were investigated.
The use of dynamic speed limits to shorten the travel time in off peak periods (FOT A1) achieves this goal. After applying the dynamic speed limit the travel time was decreased with 7%, this was beneficial for 39% of road users. An increase of NO2 emissions (0.75 μg/m3) and PM10 emissions (0.1 μg /m3) is very limited compared to the limits (40 μg /m3). The noise level per day increases by 0.3 dB (0.4 dB for the night period) and there was no measurable (negative) impact on traffic safety. If deployment is considered for this application, the (local) limits relating to air quality, noise levels and traffic safety and communication regarding these issues to residents should be taken into account.
The use of dynamic speed limits to improve air quality (FOT A58) resulted in the number of days exceeding the concentration norm of PM10 being reduced by 1.9 days from 24.4 to 22.5 days. The traffic contribution of particulate matter and NOx emissions appears to decline by 18%. The effect is smaller than expected because the average speeds remain significantly (10 to 25 km/h) above the speed limit of 80 km/h. In general, the use of dynamic speed limits to reduce the annual number of days the concentration norm is exceeded can only be successful when the traffic emission as part of the total concentration is relatively high and the current number days in exces of the concentration norm is less than 40. A better chance to succeed has the application of dynamax for the reduction of the air quality at locations with an excess of the annual average NO2 emission norm. This measure has a larger scope of application, because the contribution of NO2 traffic emissions to the (measured and calculated) total concentrations is larger. Strict enforcement is a prerequisite for effective use of the measure. Side effects are an increase in travel time by 10 to 15% and a limited (positive) impact on traffic safety and noise emissions. No additional traffic jams will emerge.
For the use of dynamic speed limits to increase traffic safety in rainy conditions (FOT A12 Bodegraven - Woerden), the deployment of the rain algorithm resulted in a reduction (12 km/h at speed limit 100 km/h and 21 km/h at speed limit 80 km/h) of the average velocity. This reduction was significantly larger than the speed adjustment road users themselves apply in the rain (3 km/h to 8 km/h).The highest speeds driven decline in a similar way as the average speeds do. The pre-determined safety indicators showed a significantly better value during the post-measurements than during the base-line measurements. The reductions in NOX and PM10 concentrations are negligible compared to local background concentrations. There is no significant effect on noise levels. The use of dynamic speed limits to decrease the average travel time by damping or solving shock waves (FOT A12 Bodegraven - Woerden), the applied algorithm has shown to solve (8%) of shock waves and thereby avoiding the emergence of new congestion. This resulted in a better throughput, an average of 39 vehicle hours lost per dissolved shock wave. At the test site this lead to a reduction of 1- 1.5% of total vehicle hours lost. The pre-determined safety indicators during the post-test showed the same or a slightly better value than the base-line measurements. In addition, solving shock waves in general has a positive effect on traffic safety. The reductions in NOx and PM10 concentrations are negligible compared to local background concentrations. There is no significant effect on noise levels. The traffic congestion algorithm can be extended in such manner that in the future more shock waves can be resolved.
The use of dynamic speed limits to improve traffic flow while preserving the positive effect of the 80 km zone for the local air quality (FOT A12 Den Haag - Voorburg) resulted in a decrease of congestion. The average number of vehicle hours lost during the evening peak decreased significantly from 622 to 215 hours. The air quality remains the same at one measurement location (in a residential area) and increases slightly at two measurement locations (near the Prins Claus Plein and the A12 junction with A4) by a higher traffic emission contribution due to the higher speed limit. This change of air quality however is smaller than the error margins of the model. The noise level appears to increase slightly by 0.2 dB and this effect is also smaller than the error margins of the model. Traffic safety does not change significantly.
The driver behaviour research shows that the dynamic speed limit is best observed and understood by displaying the dynamic speed limit on the matrix signs above each lane. It is recommended that at least speeds below 120 km/h (the current speed limit) are displayed on the matrix signs. Upon further application of dynamic speed limits a uniform use of this measure is recommended. This corresponds to the use of dynamic speed limits in the A12 FOT. The compliance of speed limits on the A1 and A58 may therefore even be larger than measured in these experiments.
An important topic regarding traffic behaviour and human factors is the reduced compliance to speed limits below 100 km/h. This is particularly attributable to situations where the speed limit does not match the current road and traffic situation from a road user’s perspective, a so called 'non credible speed limit'. In such situations compliance can be increased by indicating the reason for the desired speed adjustment on a variable message sign (VMS) accompanied by enforcement. The argumentation for throughput and air quality in such situations must be improved.
Acceptance for the different types of measures in the context of dynamic speed limits is reasonably large or large, depending on the measure. Further deployment of dynamic speed limits will be supported in most cases. Issues to be addressed regarding a nationwide deployment are mainly related to communication, the logic of (the appearance of) the measures and the enforcement of dynamic speed limits.
Based on the evaluation results it is recommended that a plan for further development and application of dynamic speed limits will be developed.
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