Default curve speed functions
For automatic speed limitation in curves, assign vehicles with the attribute Desired curve speed function the respecitve desired curve speed function (Changing the desired speed), (Attributes of vehicle types). To do so, use predefined curve speed functions, which take into account the curve speeds of different means of transport. These default curve speed functions are stored in the defaults.inpx file and displayed in the Curve Speed Functions list (Defining curve speed).
The basics of default curve speed functions
Default curve speed functions are based on data from scientific literature as well as on rules and regulations for roads in Germany (Default curve speed functions in the defaults.inpx file), (References). In addition, the following findings and assumptions have been incorporated into the definition of the default curve speed functions in Vissim:
Findings based on Schimmelpfennig & Nackenhorst and Lindenmann and Ranft 1978
- When driving in curves on dry roads, car drivers maintain high safety factors even if they perceive their driving to be just safe enough (Schimmelpfennig & Nackenhorst 1985 (References)).
- Their average curve speed is significantly lower than their perceived speed safety limit. This follows from a comparison of the findings of Schimmelpfennig & Nackenhorst 1985 with those of Lindenmann and Ranft 1978 (References).
- Even comparatively fast drivers drive slower in curves of the same radius the lower the maximum permissible speed. This has little effect when it comes to curves with small radii and speeds, but the effect increases with larger radii curves. This follows from a comparison of the findings of Schimmelpfennig & Nackenhorst 1985 with those of Lindenmann and Ranft 1978 . The comparison shows:
- At small curve radii, the drivers in Schimmelpfennig & Nackenhorst's experiment drove at about the same speed as the faster drivers in Lindenmann’s and Ranft’s study that followed a speed limit of 100 km/h.
- Starting at radii of approx. 250 meters and a speed of 90 km/h, drivers were faster in the experiment, although Lindenmann and Ranft measured v85% speeds of up to 103 km/h. For average drivers, the effect was even more significant. No speed limit applied in the experiment.
Assumptions made for the definition of default curve speed functions
- There is no speed limit specified for vehicles.
- Drivers do not try to drive as fast as possible while still being just safe, but intuitively, drive at a subjectively appropriate speed.
Adjusting data to curves
- For the middle and lower constraint functions, Schimmelpfennig’s and Nackenhorst’s function was adopted in form, but newly parameterized.
- For the upper constraint function,Schimmelpfennig’s and Nackenhorst’s function was adopted with modifications:
We adjusted the assumed cross slopes of lanes for smaller and larger radii. Schimmelpfennig and Nackenhorst measured the lateral acceleration of vehicles. In doing so, they implicitly took into account that cross slopes, at least to some extent, compensate for lateral acceleration. In other words, when drivers perceive greater lateral acceleration they tend to automatically drive faster. This observation is taken into account in default curve speed functions. Typical radii and speeds were identified for specific situations and various elements of infrastructure:
- For example, radii of up to 30 m occur mainly in urban intersections or when parking. In these cases, you cannot assume systematically supporting cross slopes. Consequently, a cross slope of 0% is then used in calculations.
- In contrast, radii of 200 m and more allow for speeds of over 75 km/h. In urban areas, this no longer leads to a reduction in speed. This is why a cross slope is assumed as specified in the guidelines for rural roads and highways. The guidelines RASt, RAL & RAA of the German Road and Transportation Research Association (FGSV) were used as a basis (References).
For details on the calculation steps visit YouTube: 
PTV Talks: Automatic Speed Limitation in Curves (PTV Vissim 2023).
You can find example files in the following default directory:
..\Examples Training\Vehicle Fleet & Settings Defaults\Curve Speed Functions
Default curve speed functions in the defaults.inpx file
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Note: Adjust functions to local conditions. This becomes particularly necessary if your vehicle fleet data significantly differs from the data the default functions are based on. |
The following curve speed functions are displayed by default in the Curve Speed Functions list:
Road. Car. Based on Schimmelpfennig & Nackenhorst (1985), Lindenmann & Ranft (1978), and German road design guidelines FGSV RASt, RAL & RAA
This function is based on data of scientific literature by Schimmelpfennig & Nackenhorst (1985), Lindenmann & Ranft (1978), as well as on sets of rules for road design in Germany: Guidelines for the Design of Urban Roads (RASt), Guidelines for the Design of Rural Roads (RAL), Guidelines for the Design of Motorways (RAA).
Road. HGV (deduced from function for cars with plausibility considerations)
This function is derived from data of the Road. Car. function. It is based on Schimmelpfennig & Nackenhorst (1985), Lindenmann & Ranft (1978), and German road design guidelines FGSV RASt, RAL & RAA.
Road. Bike. Richard; Stamminger in Meschik, following Brezina et al, adjusted for 1 m additional lateral movement in 90deg turn (inside)
This function is based on the following function and has been adapted to show the typical swerve motion of cyclists before they make a 90 degree turn.
Road. Bike. Richard; Stamminger in Meschik, following Brezina et al
This function is based on scientific literature by Richard; Stamminger in Meschik, adapted from Brezina et al
Light Rail. Design. TRStrab Trassierung
This function is based on data found in the German Technical Rules for Tramway Routing of Railways (TRStrab Trassierung)
Rail. Design. EBO
The function is based on data found in the German Railway Construction and Operation Regulations (EBO)
