How we decide when to grit the roads
Decisions are made daily, based on local forecasts and on predicted road temperatures rather than air temperatures. Salting is likely to take place when road temperatures are going to fall below +0.5 degrees Celsius.
This decision is not taken lightly. Each run uses around 65 tonnes of salt if we use a pre-wet mix, or 85 tonnes of rock salt if we lay the salt dry. The process for making the decision is as follows:
- Readings are taken from weather stations around the county. These stations check ground temperature. The decision to salt is based on the temperature of the roads rather than air. Residual salt levels are also monitored
- Daily weather forecasts are received with updates when needed. This includes graphs showing the predicted road and air temperatures. It also forecasts the status of the road surface for each 24 hour period.
- As well as the reports, experience and team work plays a big part in deciding when to send the gritters out.
Why roads may still be icy
After gritting, no promise can be given that roads will always remain clear of ice or snow. Forecasts are only prediction of the future. They are mostly very accurate, but they can change at times. Falling temperatures after rain is always a problem. It takes around 2 hours for an entire grit run. If we have to wait for rain to clear before we salt, wet roads may freeze before they are salted. We can’t salt during rain as the salt would be washed away.
In weather below -8ºC, ice will still form. The salt won’t be able to stop this.
If temperatures are near to or below zero, you should always expect ice to form on any road.
Gritters will be sent out after review of the forecast and actual conditions. They are sent at appropriate times, round the clock to ensure that roads are treated before the road temperature drops. We will try to salt before peak hour traffic in the morning and after peak hour traffic in the evening. This means the gritters are out when the roads are less busy.
The forecast will always be vital when deciding what time the gritters will go out.
If it is raining when gritters are due to begin salting, a decision may be taken to delay the run. This ensures the salt doesn’t get washed away.
Two decisions are made over gritting in Buckinghamshire. There is one for the north of the county and one for the south. This is due to a range of weather conditions and road temperatures.
Once a decision has been made, a Twitter alert is sent out. You can follow us on Twitter @tfbalerts for daily updates.
When we grit
We commit salting to a group of key roads around the county. These roads are known as Primary Routes and they’re always salted when a decision to salt is made. Primary Routes over around 44% of all roads in Buckinghamshire.
These roads consist of all A and B roads and some C and other roads.
If snowfall is due and Primary Routes have been done, we may decide to salt Secondary Routes. These routes will mostly be more minor roads that will link to roads on the primary routes, improving the network. They are also roads that will provide great access to key facilities.
In the case of a long cold spell, other roads may be salted. This occurs when all primary and secondary routes are clear of ice. This depends on salt stocks, but will rarely include urban cul-de-sacs and private roads.
We decide which roads to grit based on a scoring system, based on:
- Bends (roads over 40mph)
- Community link / residential access
- Traffic levels
- Historically salted route
- Public and School Bus Routes
- Adjacent key facilities
A road will need to score more than one of the above to pass for study. We will then decide if the point will do justice to being in primary routes.
Fully trained inspectors carry out these assessments and the routes are chosen before the winter season.
Why we prioritise
- Cost: Rock salt is given to the local authority at a cost and there is a fixed budget on deck for winter maintenance. Costs include the salt, labour, vehicles and fuel.
- Suitability: Salt works are most effective on well used roads as the tyre motion plays a key role in the process. It is a better use of a limited resource to target such roads.
- Availability: We don’t produce enough Rock Salt in this country to salt every road. This was the case in the winter of 2009–10. This was when a long period of cold weather put stress on the national salt supplies.
- Environment: We currently salt 44% of the road network. This is not deemed to have a significant impact on the local environment. Damage to plants on the side of roads is clear at the end of the season. The flow of salt into water routes is at a safe level. This would change if we salted 100% of roads on our primary routes. The flow of salt would be too high and the levels would be risky.