Traffic was moving well through Cheltenham after a morning of chaos which came with the closure of the A417, following a spate of fog-related accidents.
Cheltenham Racecourse was advising race-goers to avoid getting there via roads south of the town, due to a number of accidents, which forced road closures.
Police said it was very foggy across the county, making driving conditions testing with the A417 and A419 particularly bad.
Gates at the racecourse opened at 10.30am as planned, for the third day of races.
A spokeswoman said staff were using social media to advise drivers on the best way of accessing the race course today.
Officers are opening both sides of the A417/A419 between Cirencester and Birdlip "for the forseeable future" from 8am this morning, bringing traffic to a standstill after a crash happened.
It was expected to be fully open by noon.
On the A19 southbound entry slip from the A182, minor delays were possible due to an incident, closing one lane. Normal traffic conditions were expected from 12.15pm.
The fog has resulted in five road crashes, said Gloucestershire Constabulary, along the A417 and A419, and motorists were being advised to take additional care and avoid the area.
A motorcyclist from Frome in Somerset was being treated after his BMW bike was in collision with a Volvo car on a stretch of the road between The Granny Pump near Syde and the Cowley roundabout, near Watercombe Farm.
A police spokeswoman said the motorcyclist's injuries were serious but not life threatening.
The Highways Agency was advising drivers to allow extra travelling time for their journeys.
Their website said: "The A417 southbound is closed between the junctions with the A436 and the A429, due to an accident. Road expected to re-open from 12pm."
Another severe warning added: "The A417 northbound is closed between the junctions with the A429 and the A436, due to an accident. Road expected to re-open from 12pm."
The A417 from Cowley to the Air Balloon Roundabout is now open, after it was closed for recovery of an HGV, which was stuck near the Green Dragon Pub at Cockleford. The road was passable with care.
A police spokesman said the driver of the HGV has been reported for a traffic offence.
Thick fog across the county has been making driving conditions hazardous and police have warned that visibility is down to about 20-feet.
— Highways Agency (@HAtraffic_swest) March 13, 2014
There have been at least two crashes this morning on the A40 at Northleach, one between two lorries and a car.
Officers are requesting that vehicles use their fog lights in the current conditions to reduce the risk of more accidents, due to excess speed and poor visibility.
Earlier today, a car crashed into a bus shelter on Princess Elizabeth Way this morning.
The shelter was cordoned off by Gloucestershire Highways after a car smashed into the structure.
The white Vauxhall Astra 1.6 had mounted the pavement and crashed into the bus shelter for St Thomas More, near the junction with Hester’s Way Road, largely parking inside it.
A glass wall was shattered, leaving shards of glass on the pavement beneath.
Police and paramedics were called to the scene at around 5.50am and the woman driver was taken to the Gloucestershire Royal Hospital.