7.3 Adverse Weather, Stopping Distances & Incident Management
Key Takeaways
- Total stopping distance combines the distance travelled while perceiving and reacting with the distance covered while the brakes slow the bus.
- Speed has a squared effect on kinetic energy; load, tyre grip, brakes, gradient and weather make one invented universal bus stopping table unsafe.
- Wet roads can require at least twice the dry stopping distance and ice can require up to ten times; build the gap before the hazard develops.
- For a breakdown, make the bus visible, move it out of danger if possible, protect passengers, and never place a warning triangle on a motorway.
- After a collision, stop, assist, exchange required information and report to An Garda Síochána when the statutory conditions require it.
Heavy-Vehicle Stopping Principles
Total stopping distance = thinking distance + braking distance. Thinking distance begins when a hazard becomes detectable and ends when effective braking starts. Braking distance then depends on speed, tyre-road grip, gradient, brake condition, load distribution and the driver's use of the system. Air brakes also require the system to respond and apply throughout the vehicle.
Do not treat a table of invented “bus distances” as law. Vehicle type, mass and test conditions vary. The physics that should guide every answer is that kinetic energy rises with the square of speed: doubling speed produces four times the energy to dissipate. A few kilometres per hour removed before a hazard can therefore make a large difference. Maintain a time gap that can grow with the bus's length, load and system response, and scan far enough ahead to brake progressively.
Load changes response. Passengers and luggage add energy, while poor distribution can reduce axle grip or stability. Repeated braking on a descent can overheat friction brakes and cause fade, so select a suitable gear before the slope and use the approved retarder progressively. Never descend in neutral. If braking feel, pressure, warning indications, smell or smoke suggests a defect or overheating, stop safely and report it rather than testing the brakes farther down the hill.
Grip and Weather
On a wet road, stopping distance may be at least twice the dry-road distance; on ice it may be up to ten times as long. Increase the following gap before entering spray, standing water, frost or shade. Smooth inputs protect both grip and standing or unbelted passengers.
Aquaplaning occurs when tyres ride on water and lose effective contact. Ease off the accelerator, hold a steady course and avoid harsh braking or steering until grip returns. Tyre tread, pressure, speed and water depth all affect the risk.
A retarder can control speed and reduce service-brake heating on a long descent, but strong drive-axle retardation may cause a skid on a slippery surface. Select a suitable low gear before the descent, follow the manufacturer's instructions, and reduce retarder demand when adhesion is doubtful.
Fog, Snow and High Winds
In fog, use dipped headlights and fog lamps when visibility is seriously reduced, travel at a speed that permits a stop within the visible distance, and switch fog lamps off when conditions improve so they do not dazzle. Do not rely on a precise imported visibility number as the whole rule. In snow or ice, avoid abrupt acceleration, braking and steering and leave an exceptionally large gap.
High-sided buses are vulnerable to crosswinds on exposed bridges, coastal routes, openings between buildings and when passing large vehicles. Observe warnings, reduce speed before the exposed section, keep both hands ready for a gust and stop or divert when the operator or road authority closes a route.
Breakdown Procedure
If a defect or puncture occurs, signal and reach the safest available place without creating a greater hazard. Stop as far left as possible or in an emergency area, secure the bus, activate hazards and use sidelights or other required lighting. Wear high-visibility clothing where available and call the operator, road authority or emergency services as conditions require.
On a non-motorway road, a warning triangle should be placed at least 45 metres behind the vehicle only when it can be done safely. Never place a triangle on a motorway. Do not expose the driver to live traffic merely to meet a routine.
Passenger location is a risk decision. Fire, smoke, fuel, unstable position or a live lane can require immediate evacuation to a place behind a barrier and away from traffic. In other situations, leaving passengers inside a protected vehicle may avoid exposing them to a hard shoulder. Use the safest exit, supervise vulnerable passengers and keep a headcount.
Collision Duties
Section 106 of the Road Traffic Act 1961, as amended, requires a driver involved in an injury or property-damage collision to stop. Provide the required name, address, vehicle registration and insurance information to an entitled person or Garda and summon emergency assistance for injury.
If a Garda is not present and the required details cannot be given at the scene—for example, the owner of damaged unattended property is absent—report the collision in person at a Garda station as soon as possible and within the statutory period. Preserve tachograph and camera records, notify the operator and complete its incident process. Operator reporting never replaces the driver's legal duties.
Compared with a dry road, what can happen to a bus's stopping distance on a wet road?
On black ice or packed snow, by how much can the total stopping distance of a heavy passenger vehicle increase?
Where should a warning triangle be placed for a breakdown?
Under Section 106 of the Road Traffic Act 1961, what is the mandatory reporting timeframe to An Garda Síochána if a collision occurs and no Garda is present at the scene?