I REFER to the letter published in the Selby Times from Mr Lumb, of Wistow, and his query why the gritters were out at 8.30pm on Saturday evening (January 16) – Rubbing salt in wounds (January 21).
The forecast for the 24-hour period from noon on January 16 to midday on January 17 was a minimum air temperature of 1.5ºC and a minimum road surface temperature (RST) of -2ºC, with RSTs below 0ºC from 2am to 8am, with ice and frost forming.
The
refore, the Priority 1 routes were gritted as from 8pm on the Saturday night, following the rain that had been forecast, in preparation for the sub-zero forecast event.
The lowest actual RSTs were recorded as -2ºC and the air temperature as +3ºc about an hour before day break, as predicted, and black ice formed on surfaces that hadn't been treated the night before.
Although Mr Lumb may not have risen until later in the morning, there are others who are up and about before dawn using the highway network, when conditions were far from bright and sunny.
Any gritting action is determined by RSTs and not air temperatures. As can be seen, RSTs can be much lower than air temperatures, and ice will form on road surfaces even if the air temperatures are above 0ºC. The recorded air temperature at 8.30pm on the Saturday night was 5ºc, a lot lower than Mr Lumb had indicated in his letter, with RSTs dropping quickly after 9pm.
I hope this clarifies the concerns raised by Mr Lumb.
Paul Sheppard, NYCC
highways and transportation
Selby area manager
