Variable speed limits: Evaluation of the road weather controlled section Trials with Variable Speed Limits (VSL) for The sections differ from each other. The site different applications are carried out by the in Halland is a fairly traffic intense highway Swedish Road Administration (SRA). The (18000 vehicles/day) while Blekinge is a three goal is to demonstrate if and how VSL can lane highway with centre crash barrier (2+1) contribute to a better speed adaptation in a and average daily traffic of approximately cost-efficient way. Road weather controlled 8500 vehicles/day. sections are one application area. For this type of application the maximum allowable The evaluation programme involves the fol- speed limit is adjusted downwards to diffe- lowing main activities: rent levels when adverse weather and road • Follow-up analyses of operational data surface conditions occur. Preliminary results • Measurements and analyses of traffic data from the first trial period are presented in (traffic counts, speed- and performance this report. studies) • Driver attitude surveys (questionnaires in Road weather stations (RWIS) at the trial si- Blekinge and Halland) tes collect weather data from the air as well • Cost-benefit analyses (including impact as above and under the road surface. These assessments regarding traffic safety, tra- data are processed by a weather model at vel time and environment) the SRA Head Quarters from where alerts • Scanning (international experiences, etc) signals are sent to the regional Traffic infor- mation centre (TIC). Operators activate the Operational follow-up Variable speed limit signs (VSL signs) with The technical equipment functioned satis- shining white figures in a red ring on dark factorily except for the communication sys- background resulting in a change of the dis- tem in Blekinge. Due to the problems in Ble- played speed limit. Every step is logged and kinge the accessibility measure, meaning the the information is transmitted to a central share of time when all VSL signs could be data-base. correctly controlled at adverse weather con- ditions, was only registered to 62%. In Hal- The trial sites included in the report are a 17 land however the technical km section of E22 in the province ofBlekinge accessibility measure was 99.2 %. Due to (Åryd-Ronneby), 55 km of E6 in Halland wind sensor problems at the Uddevalla site, (Skottorp–Heberg) and the Uddevalla Bridge. incorrect values were registered. This sensor The first mentioned two establishments are is now disconnected. controlled based on the road surface condi- The sign control procedure did not work ful- tion and the Uddevalla Bridge is controlled ly satisfactorily. There are quality drawbacks based on crosswind. in the operator support systems (such as the weather model, RWIS-data etc). ploughing and salting mission. This might take long, especially at night, before the contractor has moved to the site. During that time the speed limit might be insuffi- Since data from RWIS are delivered in 15 cientlyThe decreased increase by the operator althoughof the the conditions maximum call for lower limits.permitted This might give the drivers a false message. Improvements are needed. minutes cycles, alerts from the weather mo- speed limit in Blekinge from 90 to 110 km/h Traffic impacts del arrive late and there could be big jumps Trafficmade data were collectedthe average in pre and pos t studiesspeed carried to out duringincrease two consecutive by 4-5 winter seasons. A second follow-up was accomplished in Blekinge a year later to in suggested levels. Contacts with the road observekm/h. the long termThis effects. is also valid for Uddevalla alt- maintenance contractor are needed for con- The speedhough adaptation there was clearly was improved no by raisethe VSL system of theat both speedsites (Halland limit and Blekinge). This is especially true for passenger cars. The most evident impacts firmation of indicated severe road surface occur there.at low speed Thuslimits. The averagethe speedobservance is then 15-20 km/h of below the the level highest that the drivers choose during corresponding adverse conditions with traditional fixed conditions (levels 80 and 60 km/h) and for signs.speed See figure below.limit increased. In Blekinge the ob- information about completed ploughing and The averageservance speed in Halland of increasedthe speed only by 2 km/hlimits during goodalso conditions improved salting mission. This might take long, espe- despitewhen the fact that wet the highest road speed limitsurface was changed or from snow 110 to 120 (displayedkm/h. One might speculate why it did not increase more. One reason could be that it is unclear to cially at night, before the contractor has mo- the drivers100 where and the VSL90 systemkm/h starts respectively). and ends. Another explanation could be that they consider the speed limit around 110 km/h to be comfortable. ved to the site. During that time the speed The increase of the maximum permitted speed limit in Blekinge from 90 to 110 km/h limit might be insufficiently decreased by the made Howeverthe average speed theto increase observance by 4-5 km/h. This isof also the valid forlowest Uddevalla speed although there was no raise of the speed limit there. Thus the observance of the operator although the conditions call for lo- highestlimits speed limit at increased. severe In Blekinge road the observance surface of the speedconditions limits also de- improved when wet road surface or snow (displayed 100 and 90 km/h respectively). wer limits. This might give the drivers a false Howevercreased the observance as of expected. the lowest speed limits at severe road surface conditions message. Improvements are needed. decreased as expected. 120 120 Halland before Halland after Blekinge before Blekinge after Traffic impacts 110 110 110 110 110 110 110 110 Improved speed Traffic data were collected in pre and post adaption with VSL, studies carried out during two consecutive 100 100 100 14 km/h and 20 km/h winter seasons. A second follow-up was ac- 90 90 90 90 90 90 90 complished in Blekinge a year later to obser- ve the long term effects. The speed adapta- 80 80 80 tion was clearly improved by the VSL system 70 at both sites (Halland and Blekinge). This is 60 60 60 especially true for passenger cars. The most Dry surface Wet surface Snow Ice Severe ice evident impacts occur at low speed limits. Figure: Average speeds at Hökaslätt in Halland and Bräkne-Hoby in Blekinge (both directions) at Figure:different road Average surface conditions speeds with and without at VSL Hökaslätt in Halland The average speed is then 15-20 km/h below and Bräkne-Hoby in 80Blekinge (both directions) the level that the drivers choose during cor- at different road surface conditions with and responding adverse conditions with traditio- without VSL nal fixed signs. See figure below. It can be concluded that the VSL system gives The average speed in Halland increased only a minor contribution to better speed adapta- by 2 km/h during good conditions despite tion at fairly difficult conditions. At hard and the fact that the highest speed limit was very rough conditions (snow, ice, and severe changed from 110 to 120 km/h. One might ice) the VSL system gives significant extra speculate why it did not increase more. One stimuli to the drivers to adjust their speed reason could be that it is unclear to the dri- properly. vers where the VSL system starts and ends. Another explanation could be that they con- Long time measurements were conducted sider the speed limit around 110 km/h to be in Blekinge one year after the first measu- comfortable. rement period with the system operational. The results show a continuing decrease of database STRADA state that the number of the average speed to an even lower level than accidents with injuries increased from 4 to during the first follow-up period. This is es- 13 during the first three years and that the pecially evident when 60 km/h is displayed. number of fatalities and severely injured in- creased from 1 to 2 individuals after the in- Attitudes troduction of a raised maximum permitted The drivers´ respect of the speed limits speed limit and VSL. However the follow-up strengthened with the introduction of VSL. periods are far too short. Thus it is important In total, more than 90 % of the respondents to continue the accident analyses over longer in Halland and about 70 % in Blekinge consi- periods of time. der the system to be good. The most frequent comment to why the system is good is that Performance it contributes to a more harmonised traffic The idea behind weather controlled variable flow. About 80 % of the drivers believe that speed limits is to be able to accept higher they have become more attentive regarding speeds at good conditions (dry surface) as a the road surface when passing an activa- trade off for differentiated speed regulations ted VSL sign. A majority of the respondents during periods with adverse weather and in both surveys also believes that display- road surface conditions. In Halland the time ed speed limits are in line with the current consumption decreased by 1.3 % while using weather and road surface conditions while VSL in combination with a raised maximum about one third disagree to this. Almost half speed limit. The corresponding figure for Ble- of the drivers in Blekinge thus consider the kinge is 1.4 %. Thus the impact on time con- signs sometimes being out of order or that sumption is minor. the wrong speed message is displayed. Re- gardless of the reason behind this opinion, it Environment is important to display speed limits that are The environmental impact from VSL is mar- apprehended as correctly as possible with ginal.