#27 Raised Safety Platform Ramp Gradient
- Duc Phan
- Jun 16
- 2 min read
As outlined previously in Post #16, raised safety platforms (RSPs) are a primary Safe System treatment to promote lower vehicle speeds to reduce the likelihood and severity of collisions. RSPs are vertical deflection devices suitable for a wide range of roadway and traffic characteristics. A 2020 Austroads Research Report (AP-R642-20) documents RSP effectiveness and implementation in detail. Among the many considerations for design and implementation, the gradient (slope or angle) of approach and departure ramps is a critical factor which determines the extent of speed reduction. Close attention must also be paid to the severity of ramp slopes to achieve the desired effect without unduly disrupting the comfort and controllability of vehicles of different types.
Tailored Solutions and Specifications
Different specifications are advised for different speed zones, vehicle types and roadway characteristics. Higher platforms and steeper approach ramp gradients generally lead to greater levels of speed reduction. These are typically used in low-speed areas with high vulnerable road user (VRU) volumes, while less severe slopes are used in higher speed zones (up to 70km/h). Departure ramps may be less steep than approach ramps (advised) as speed reduction is more associated with the approach ramp while less severe departure ramps provide greater comfort and controllability.
Depending on the road speed and ramp target speed, approach ramp gradients generally range from 1:10 to 1:30, while departure ramps may extend to 1:35 in some cases. Platform height generally ranges from 75 – 100mm, and minimum flat-top length from 2 – 7m (excluding raised intersections).
Design guidance for RSPs (adapted from Austroads Guide to Road Design Part 7)
RSP approach gradient | Operating (road) speed (km/h) | Ramp target max. speed (km/h) | Considerations and potential negative effects |
1:10 – 1:15 | 40-50 | 30 | Severe slope may disrupt buses, trucks, emergency vehicles, low clearance cars. |
1:20 | 60 | 40 | Balancing speed reduction with comfort. VRU Safe System collision speed not met*. |
1:25 – 1:30 | 70 | 50 | Gradual slope diminishes speed reduction effects. |
*30km/h is generally considered a survivable impact speed for pedestrians and cyclists
Other Considerations
More detailed evaluations are needed on specific impacts on different road user groups, vehicle types and services. Specifications and requirements differ according to other road characteristics such as divided/undivided, number of lanes, vertical and horizontal alignment, and sight distance, among others. Potential for heavy braking and rear-end crashes at RSPs is acknowledged in research but not considered significant.
