Sight distances

Pedestrian crossing facilities should be located and designed such that there is a clear view between approaching drivers and pedestrians on the crossing or waiting to cross the roadway.

The longer the distance to cross, the less likely I will enjoy that part of my walk. I have to keep looking over my shoulder to check no more traffic is coming, it is very stressful. Aisha

Guidance on sight distance at crossings for people walking is provided in various sections of the Austroads Guide to Road Design Part 4A: Unsignalised and signalised intersections [1] and is provided below for ease of reference.

There are two key sight distance requirements at pedestrian crossing facilities:

• Approach sight distance (ASD) ensures that approaching drivers are aware of the presence of a crossing. The line of sight must not be obstructed as it ensures that the driver is aware of the crossing by seeing the pavement markings and other cues even if there is no pedestrian on the crossing, and is therefore alerted to take the appropriate action if a pedestrian steps onto the crossing. ASD should be provided at all formal, marked pedestrian crossings.
• Crossing sight distance (CSD) ensures that people about to cross can see approaching traffic in sufficient time to judge a safe gap and cross the roadway. It also ensures a clear view for approaching drivers to see people waiting to cross the road.

CSD should be provided at crossings, including:

• • where the pedestrian does not have the priority, or
  • where the pedestrian has the priority and must be seen by approaching drivers/riders who must give way (e.g. a zebra crossing).

CSD is desirable at crossings controlled by signals in case of signal failure.

The figures below illustrate the sight distance requirements at crossings.

Sight distance requirements at pedestrian crossings.[2]

Crossing sight distance

Crossing sight distance (CSD) should be provided between approaching vehicles (1.1m eye height) and a pedestrian waiting to cross the road (waiting 1.6m from the pavement edge or kerb line). The pedestrian eye height should be taken as 1.07m which accounts for a child or a person using a mobility device. CSD allows sufficient time for the pedestrian to cross the road, clear of any approaching traffic.

CSD is calculated from the critical safe gap in the traffic stream and the speed of approaching traffic using this equation:

Where:

• t_c is the critical safe gap (sec) = (crossing length/walking speed) + 3 sec for pedestrian start up and end clearance time
• V is the 85th percentile vehicle approach speed (km/h).

Notes:

• Average walking speed is 1.2m/s; however pedestrians walk at different speeds and designers need to consider the type of pedestrians likely to use the crossing and their likely walking speeds.
• The crossing length shall include the pedestrian set back (e.g. 1.6m from pavement edge or kerb line).
• The 3 seconds for pedestrian start up and end clearance time allows for decision making and navigating the kerb ramps, but may not be achievable in constrained situations. A risk assessment should be undertaken if the 3 sec start up and end clearance time is omitted.

It is important that line of sight for CSD is not impeded by objects such as parked vehicles and street furniture (although minor obstructions such as poles and tree trunks less than 200mm diameter may be ignored). Parked vehicles can cause visual obstructions, especially for children, and people using mobility devices. This may require restricting  parking for some distance on each side of the crossing to ensure parked vehicles will not obscure the required sight lines. Where on-street parking needs to be maintained, kerb extensions at the crossing should be provided to improve the visibility of pedestrians.

Approach sight distance

Approach sight distances should be measured from the driver eye height (1.1m) to ground level (0m), which ensures that a driver is able to see any pavement markings and other cues at a crossing, and therefore be alerted to take the appropriate action if a pedestrian steps onto the crossing.

Approach sight distance (ASD) is calculated by:

Where:

• R_T is the driver reaction time (seconds), equal to 1.5 sec where drivers will be alert (eg. in an urban area)
• V is the 85th percentile vehicle approach speed (km/h).
• d is the coefficient of deceleration, generally equal to 0.36
• a is a longitudinal grade in % (in direction of travel: positive for uphill grade, negative for downhill grade).

Note: Austroads Part 4A provides correction factors to account for road gradient if necessary.

Values of ASD based on the above equation and for different vehicle speeds and no gradient are listed in the table below.

Table: Minimum approach sight distances

Note in rural locations driver reaction times may be slower. The Austroads Guide to Road Design Part 4A includes approach sight distances assuming slower reaction times which may be more applicable in these instances.

The approach sight distances listed in the table above presume emergency braking and adequate skid resistance. It is important to assess the skid resistance of the roadway on the immediate approaches to a pedestrian crossing point. Treatment is justified if the skid resistance (sideways force coefficient) is less than 0.55.