While last winter was milder in comparison with previous ones, marginal temperatures meant winter service teams have been kept busy. Jon Masters reports.
Prolonged periods of cold weather over the past winter appear to have placed the 2014/15 winter service season in the ‘about average’ category. Few instances of exceptionally low temperatures or heavy snowfall overall have resulted in the year passing without serious alarm, but gritting teams were a lot busier this year than the previous unusually mild 2013/14 season.
A feature of the 2014/15 winter was temperatures hovering at the margins of triggering gritting runs. Forecasts resting on probability of cloud cover will have resulted in roads being treated unnecessarily in some instances.
So can it be done better? Gloucestershire CC will be looking for ways to improve efficiency with its new service provider Amey for next year, says the council’s area highways manager Jenny Goodson. Gloucestershire carried out 87 key route gritting runs during 2014/15, which compares to the county’s five-year average of 72 annual outings for its gritting crews.
‘We had a lot of marginals this year, which led to quite a lot of operations or occurrences where in hindsight we shouldn’t have gone out. It was a difficult year to forecast, partly due to changes in cloud cover from that expected. Predictions of zero or sub zero temperatures didn’t come about in some cases. We’ve carried out a forecaster report with Amey and found that similar issues were encountered elsewhere,’ Ms Goodson says.
There is understandably a level of conservatism in the approach taken to highway authority winter service operations. The opposite effect, where gritting is not done when it should be, does not happen, says Goodson. Excessive caution can cause roads to be treated too early though, which reduces its effectiveness.
‘Over the last few years, we’ve ended up doing more gritting runs than our 10 year average of 67 annual outings. This is likely to be down to having a greater number of weather stations and a result of forecasting technology getting better,’ Ms Goodson says.
Other ways may have to be found to reduce costs. Changes for next season are being looked at with Amey in Gloucestershire, including the possibility of an additional depot to shorten gritting routes. ‘We’re always looking for more efficiency. More cuts are coming, not specifically to our winter service budget, but the expectation is for reductions across the board, which means we need to look at opportunities for savings, especially with regard to vehicle fleets and costs per given routes,’ says Ms Goodson.
On Transport for London’s (TfL) red route network, 2014/15 was a busier year for gritting crews than the previous season, but still a mild winter compared to the average, says TfL senior route manager Robert O’Rourke.
‘We gritted more this season than last, but 2013/14 was an exceptionally mild year and we’ve recently spent only two thirds of the winter service budget compared to the annual average,’ Mr O’Rourke says.
A relatively snow free year in London has meant that the snow desk in TfL’s traffic control centre, and its protocols for snow clearance and getting buses out of depots and onto the road network, were not called upon this year.
‘Efforts to improve responsiveness will naturally tend to receive less attention when we’re getting mild winters,’ says Mr O’Rourke, who chairs LoTAG’s winter service practitioners group. ‘Generally, however, we’re seeing some focus on local community work and training of snow wardens across the London boroughs.’
TfL is continuing to apply rock salt on the red route network, but has introduced use of CMA (calcium magnesium acetate) on key structures.
‘We’re also considering using liquid de-icers on cycle routes where these are segregated, to protect street furniture,’ Mr O’Rourke says. ‘Regarding Appendix H, we’ve been testing and measuring salt moisture content where it’s stored and calibrating gritters to get reduced spread rates. Gains have been marginal, giving us 8g/m2 instead of 10g/ m2 but the calibration and throw tests certainly help, particularly when temperatures are very cold.’
A single weather forecasting service has now been procured by TfL, Mr O’Rourke adds, principally to save costs and ensure a consistent message. ‘There is nothing particularly new or unusual about this service. Sensors give carriageway information backed up with infrared measurement, but this only provides information for a given point. This is where thermo-mapping is helpful, using historic data to profile temperatures across larger areas,’ Mr O’Rourke says.
So how do authorities know they are getting it right? TfL has no formal means of getting feedback, says Mr O’Rourke. ‘All TfL gritters are fitted with GPS tracking, so we know precisely what roads were treated and when, but we have no formal means of determining how effective those treatments were,’ says Mr O’Rourke.
Like most authorities, TfL’s key performance indicators only measure how successfully gritting was carried out within given time periods.
East Sussex County Council has been addressing this question and has come up with a new scientific method of measuring performance.
‘We wanted to know whether we’re really doing a good job with our winter service, whether it’s money well spent. How can we measure success and get confidence we’re doing the right thing? Inevitably budgets are getting tighter and we have to justify spending millions on treating roads,’ says ESCC head of high- ways Roger Williams.
East Sussex has recorded a very cold 2014/15 and a very busy winter service season. According to Williams, this February was the coldest in the county since 1998, on the basis of the number of days below freezing, with temperatures down to -7 degrees C.
‘We overspent our budget this year, having carried out 44 gritting runs when we budgeted for doing 32. We didn’t get any snow but cold temperatures had a significant impact. We can justify why we provide a winter service but how do we know how good a job we’re doing?’ Mr Williams says.
The answer, developed with Vaisala, is a series of non-invasive road sensors installed at five locations across the county. These give a ‘grip’ reading by measuring surface temperature and layer thicknesses of water, ice and snow.
‘In the normal sense engineers will understand a measure of grip in terms of friction testing, but what we’re talking about for assessing winter service is the affect of weather on traction,’ says Vaisala road and rail solutions manager Rachel Adams.
The grip measurement was derived empirically from road temperature and surface state in Finland early on in development of Vaisala’s sensors, Ms Adams says. The next stage involves turning this into a winter performance index (WPI) which came out of work done by the company with the Idaho Department of Transport (IDoT) in the United States.
‘Idaho had 105 weather stations and high costs and was experiencing more accidents than expected due to snow and ice. IDoT developed an algorithm to calculate WPI from measurement of grip, wind speed, surface temperature and thickness of ice and snow. We helped them automate the whole process,’ Ms Adams says.
There are further levels of complexity in the whole process, such as recording and measurement of the severity and treatment of different types of event.
‘But essentially, what we’re looking for is zero WPI as a perfect performance score, or in other words, there was an event but treatment was applied to maintain surface grip,’ Ms says Adams.
‘This system is not for deciding when to treat or how much salt should be applied. That’s for the authority or service provider to decide. But it does give a scientific measure of performance on road surface condition.’
The system has achieved a level of satisfaction in East Sussex. ‘It has without doubt worked in my mind,’ Mr Williams says. ‘It’s confirmed two things: It’s given a value to attach to the work we do on winter service; plus it allows decision makers confidence that they’re doing the right thing.’