Police are to investigate why so many pedestrians and cyclists were killed on Oxfordshire's roads last year.

Although deaths on the county's highways halved in 2007 compared to the previous year, a "disproportionately" high number of casualties were not in a vehicle.

Out of 34 casualities, 20 were pedestrians, motorcyclists and cyclists.

Police now want to get to the bottom of why what are described as "vulnerable road users" accounted for more than two thirds of fatalities.

Malcolm Collis, head of road safety for Thames Valley Police, said: "We are looking at whether there is a cluster of accidents, if people are getting knocked down on a particular crossing, whether it's a particular town or if it's just random.

"We are also looking at the age and gender of victims, the time and place and time of the week. We want to see if there are any patterns.

"We can't just sit back and do nothing but we're not going to cure it overnight."

Last year, pedestrians Andrew Edwards and Christine Diacon died crossing roads in Witney and cyclist Tsz Fok died in Oxford.

Deaths across the Thames Valley fell from 143 in 2006 to 118 in 2007 - but the number of cyclists killed doubled and pedestrian fatalities were at a six-year high.

Half of the 10 cyclists killed across the region died in Oxfordshire.

And police figures showed that although motor- cyclists accounted for just one per cent of journeys, they represented 18 per cent of fatalities in the Thames Valley.

James Styring, chairman of Oxford-based cycling pressure group Cyclox, said: "To hear that five cyclists have died is a surprise.

"It's very sad and rather shocking. I can only hope and assume it's a spike in the statistics.

"But for the number of journeys people make on bikes - particularly in Oxfordshire - it's not a dangerous activity."

Mr Styring corrsaid the statistics backed up a plan to reduce some speed limits within Oxford's ring road to 20mph.

He said research by the Life Begins at 20 campaign showed driving at no more than 20mph added between 30 seconds and two minutes to a journey from the ring road into Oxford city centre.

He added: "The disadvantage of a 20mph limit on drivers is negligible - but the difference to the people who are likely to be victims of accidents is huge."