Why are some roads treated and some are not?
Our 36 vehicles grit 52 per cent of the road network. Suffolk is a large geographical area and weather conditions and road surface temperatures can vary across the road network on the same night. Suffolk has therefore been divided into 4 domains (West Suffolk, Central Suffolk, Ipswich and Coastal) and each of these domains has a separate weather forecast based on weather station data (there are 11 weather stations around the county) and treatments are tailored to different weather conditions. Therefore, there may be occasions when we grit some parts of the county but not others.
How do we decide when treatment is needed?
At midday every day during the winter period (1 October to 30 April), our team of decision makers receive a weather forecast. Treatments are planned on a forecast of a road surface temperature trigger of 1 degree C or less - this is different to the air temperature which can be noticeably higher. They use the forecast to decide whether to send out the gritters, in which areas and how much salt needs to be spread. We check the forecast at 5am, midday, 6pm and 11pm to help us make the decision about when to go out or to alter any previous decision as road surface temperatures can dip below 1 degree C overnight. Our gritters will usually go out after evening rush hour when the roads are quieter – but can go out throughout the night depending on the weather. We aim to complete all salting 1 hour prior to the onset of the hazard.
Why are some gritters not spreading salt?
Our gritters are far more sophisticated than they were years ago. Rather than spraying salt in all directions, the computer-controlled mechanics now dispense the required amount of salt directly down on to the road and can do so at a certain angle. The drivers can control the direction of salt and the width of spread to ensure the whole carriageway is covered even if the vehicle is driving down one side only. This also happens on a roundabout.
Gritters won’t start gritting the moment they leave the depot – all our drivers have specific routes and the vehicle may not have reached the starting point of its treatment route or may be returning to the depot at the end of its route or to refill. Gritters may also cross or part drive roads on other routes, when this occurs the gritter will cease treating. Once they return onto their prescribed route they will commence treating again.
Each gritting vehicle has a GPS system which tracks its route, speed, whether it is spreading salt, and if so, the amount being spread. The date and time a vehicle was on a certain road and what it was doing is always recorded. Drivers will alert the Duty Manager at each depot should there be a road closure and the vehicle need to deviate from its usual route.
Does salting on a road prevent the formation of ice?
Spreading salt on the roads lowers the freezing point of water, helping to stop ice from forming. However, in exceptionally low temperatures (below -8C), salt may have little or no effect. Always check the advice of the emergency services before heading out - even when roads have been gritted, road users must still travel with care as the roads may still be slippery.
Does the county have enough salt?
The county has the capacity to hold sufficient stock for an average winter. We will start the winter season at full stock capacity which is approximately 22,700 tonnes of salt, more salt can be ordered in if required.
What type of salt is used?
De-icing salt 5mm sodium chloride (rock salt) in compliance with BS3247:2011
How do you ensure that Suffolk Highways does not run empty on salt?
We have a constant record of how much salt we currently have, and we are in contact with national suppliers to monitor deliveries. Stock levels are recorded on a regular basis throughout the winter season and reported to central government. The stock information provided to central government has been used to ensure that deliveries of salt are distributed to the local authorities who are most in need of supplies to prevent authorities running out of salt at times of shortage.
How is salt effective?
Water freezes when it reaches 0C. Salt mixed with water or moisture lowers this freezing point. The colder the temperature and the more water present, the more salt is required to lower the freezing point. The effectiveness of salt begins to lessen at about -3/4C, and by -6C the quantity of salt required to remove snow or ice becomes ineffective. A small handful of salt (approximately 20g) can treat approximately 1m/3ft squared of cleared surface. If snow and ice have already formed on the roads and pavements, then adding salt will not help because there is no direct moisture for the salt to dissolve into. Snow and ice must be manually removed first.
What has been the salt usage for the last few years?
- 2013-14 – 9,471 tonnes
- 2014-15 – 15,685 tonnes
- 2015-16 – 8,465 tonnes
- 2016-17 – 12,547 tonnes
- 2017-18 – 28,097 tonnes
- 2018-19 – 10,585 tonnes
- 2019-20 – 7,989 tonnes
- 2020-21 – 21,223 tonnes
If the treatment has been undertaken, why is there still snow and ice on the road?
Treating the roads and spreading salt does not guarantee that the roads will be free from ice and snow. Salt requires the friction of the traffic to work it through the snow. Salt works by reducing the freezing temperature of water. Snow and ice are solids that need to be broken down/melted by traffic movement. On quiet roads, there may not have been enough traction to ‘activate’ the salt.
Our larger gritting lorries can be fitted with snow ploughs and are used as required to remove the heavy dumping of snow from the roads. The plough must have a clearance above the road to protect the road surface and to ensure the vehicle can manoeuvre around. This does leave a layer of snow on the roads. No guarantee can be given that roads will always be completely clear of ice or snow.
What's the duration of a treatment?
We aim to complete each grit run within 2.5 hours. This is timed from the depot gates to the end of the gritting route.
What should I do if a salt spreader was travelling too fast to be safe?
Contact the Customer Service Centre on 0345 606 6171 and tell us when and where this happened, and we will investigate your concerns. When spreading, salt spreaders should travel at no more than 35mph.
How many miles do Suffolk Highways treat?
Approximately 1,259 miles / 2,015 kilometres.
Does Suffolk Highways carry out private gritting?
Suffolk Highways does not undertake the salting of private roads or non-highway areas except in exceptional circumstances where there are a high number of vehicle movements to an individual location such as a hospital or bus station.