Models of vehicle operating speeds along two-lane rural highway transition zones: panel and multilevel modeling approaches
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AbstractAbstractTransition zones are defined as locations where the posted speed limit changes from high- to low-speed. On high-speed two-lane rural highways, transition zones are often encountered when the roadway approaches a built-up area. The purpose of this study was to collect operating speed, roadway, roadside, traffic control, and land use data along two-lane rural highway transition zones in central Pennsylvania. These data were used to estimate passenger car operating speed models, recognizing the hierarchical nature of the data-generating process. The results showed that a three-level model could capture site-level speed variance that could not be captured in a panel data modeling framework; however, the parameter estimates and standard errors were very similar when comparing the model estimation results. It was also found that the presence of horizontal curves, presence of warning signs, the presence of curb, and increased access density were associated with reduced vehicle operating speeds. Increasing the lane width, shoulder width, and lateral clearance to obstructions was associated with increases in vehicle operating speeds. The models estimated in this paper could be used as a starting point to develop transition zone design guidelines.Keywords: vehicle operating speedrural highwaytransition zonesspeed limitKeywords:
Speed limit
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Using design speed as a primary consideration for selecting the speed limit of a freeway has been a common practice since the opening of the first freeway in China about twenty years ago. This practice has been widely questioned and challenged in recent years by the public, freeway operators, and law enforcement. Speed limits solely based on the location specific design speed in many newly completed freeways in the country have been under intensive public scrutiny, particularly at locations where the operating speeds are much higher or lower than the speed limits. One key consideration in establishing speed limit is the operating speed that closely relates to driver behavior, vehicles' mechanic properties, and the design speed. Driver behavior varies greatly by factors including cultural background and stage of economic development. Undoubtedly different social, economic, and cultural environments contribute to significant variation in driver behavior. The methods used by developed countries in speed limit selection may not be suitable, or at least not entirely applicable, to situations in developing countries. Thus, as part of a project sponsored by the Chinese Ministry of Communication, the goal of this study is to investigate the relationship between speed limit and operating speed in different freeway environments. The principal findings from the study are: (a) operating speed is only loosely associated with speed limit, (b) for a given speed limit, the average speed varies greatly depending on the characteristics of the location, (c) standard deviation of operating speed distribution on freeways in China is generally much bigger than on a typical freeway in developed countries, and (d) there are huge speed gaps between small and large vehicles. The last two findings represent a big safety problem for freeway transportation. The combination of speeding and slow running vehicles on freeways significantly lowers freeway capacity, as well. The unique speed characteristics observed by this study prompts a few suggestions on speed limit and speed management.
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Speed limit
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Unreasonable speed limit caused by the lack of coordination of operating speed and posted speed can be a major contributor to traffic accidents. Operating speed reflects operating conditions displayed by actual traffic and is closely related to the location of the highway, geometric design, traffic volume, traffic composition, driver skill, traffic management facilities, traffic safety facilities and roadside environmental factors.. According to current research abroad, the 85th percentile operating speed, V85, is usually greater than the posted speed limits. The relevant information of the ordinary provincial arterial highway was based, and the relationship between operating speed and posted speed limits on straight road sections is finally researched. Operating speed V85 of the car is greater than limit speed, and truck operating speed V85 is almost the same as the limit speed value, even below the limit speed value.
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The paper emphasizes that posted speed limit does not directly have impact on accidents. On the contrary, it influences traffic safety through operating speed. Therefore, it's essential to explore the relationship between them. In this paper, the conditions of the same posted speed limit were analyzed. In addition, some comparisons between 1st-class highways and 2nd-class highways about operating speed were made. It can be found that posted speed limit significantly impact on operating speed. The operating speed is usually larger than the posted speed limit. With the change of the posted speed limit, the operating speed reduces or increases accordingly.
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The objective of this research was to examine the relationship among design speeds, operating speeds and speed limits and address safety and operational concerns regarding the presence of disparities among these speed metrics. Roadway sections were selected throughout Kentucky based on the relationship between design speed and posted speed limit (greater or lower) and on the number of lanes (2 or 4). Speed data and roadway geometry data were collected along these sites to allow for the development of the appropriate models. The general conclusion for 2-lane highways is that the operating speed is different than the design speed indicating that there is no agreement between them. For the 4-lane highways there was an agreement between operating and design speeds indicating the absence of any differences. The relationship between operating speed and posted speed limit showed that for all roadways these two speed metrics were different and the posted speed limit was lower than the 85th operating speeds. The safety analysis showed in general that there were no significant safety consequences from the inconsistencies among the various speeds metrics. A set of recommended guidelines is proposed that aim in alleviating potential inconsistencies among these speed metrics focusing on selecting the design speed based on desired operating speeds to avoid possible inconsistencies that could lead to driver errors.
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The relationship between posted speed limits and operating speed is one of the main factors in determining appropriate speed limits in a speed zone. In this research, 19 sites were randomly selected from the 3rd, 4th, and 5th Express Ring-Road in Beijing, and the spot speed and headway data were collected at these sites. Then, free-speed data were reduced from the original data, and the 85th percentile speeds were computed as each site's operating speed. Deviation analysis of operating speed at the 3rd and 4th site shows that there were no obvious distinctions between these two types of road facilities. The regression analysis of posted speed limits and operating speed shows that there exists a strong linear relationship between these two speed terms. The percentage of operating speed exceeding posted speed limits increases with the speed limit value. The relationships between speed limits and operating speed established here may be expected to provide some quantifying basis for transportation agencies to set posted speed limits in speed zones. Results of this study may help the Department of Transportation and its districts quantify the speed limits and provide more objective insights for setting speed limits.
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In order to find the relationship between posted speed limits and operating speed in urban expressways,19 sites were randomly selected from the 3rd,the 4th and the 5th Express Ring-road in Beijing and the spot speed and headway data were collected at first.Then,free-speed data were reduced from the original data according to certain principles.The regression analysis of posted speed limits and operating speed shows that there exists strong linear relationship within these two speed terms.The percentage of operating speed exceeding posted speed limits increases with the speed limit value.The relationship between speed limits and operating speed established here was expected to provide some quantifying basis for transportation agencies to determine the posted speed limits at speed zones.
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Setting reasonable speed limits is an efficient measure to improve the safety of freeways in mountainous areas. Twenty-five typical sections randomly selected from Xihan Freeway and Qinglian Freeway in China were investigated. On the basis of analyzing the data of 25 sections, speed distributions for cars and trucks under different speed limits were obtained. The correlation between operating speed and posted speed limit of mountainous freeways is analyzed. By means of regression analysis, the relationship model between the 85th percentile speed and posted speed limit, 50th percentile speed and posted speed limit, 15th percentile speed and posted speed limit are established respectively. The regression analysis of posted speed limits and operating speeds shows that there exists a strong linear relationship between these two speed concepts. The 15th percentile speed model is the best fitting model among the three.
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Posted speed limit doesn't have direct impact on accidents,but on the contrary,it acts on the road safety through its influence over the operating speed.Therefore,it is essential to analyze the relationship between them.In the conditions of the same speed limit value,there are some comparisons between 1st-class highways and 2nd-class highways about operating speed.It can be found that posted speed limit has significant impact on operating speed,and the operating speed is usually larger than the posted speed limit.With the change of the posted speed limit,the operating speed can reduce or increase accordingly.
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Electronic speed control
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