Nine people were killed and 84 suffered serious injuries in road traffic collisions in the Horsham district between April 2013 and March 2014.
Road safety figures produced by West Sussex County Council reveal that only roads in the Mid Sussex district are more dangerous than Horsham within the county.
A total of 109 people were killed or seriously injured on Mid Sussex roads during the period of time - compared to 93 in Horsham.
The Mid Sussex district is also larger in size than the Horsham district.
The figure drops to 52 in the Worthing district and 34 in the Crawley district.
Inspector Phil Nicholas of Sussex Police’s road policing unit said: “While it seems a worrying upward trend in seriously injured casualties in the Horsham district, this should also be seen in light of the previous years, which shows we have had a high reduction in casualties.
“One fatality on our roads is one too many.
“Making further reductions in casualty rates year on year, on the back of significant past reductions becomes increasingly difficult but this is something that we are committed to.”
A further 342 people received slight injuries in road accidents to take place in Horsham.
In West Sussex there were 30 fatalities on roads within the period of time, while 450 people received serious injuries and 2195 slight injuries.
Insp Nicholas added: “Sussex Police continues to work with the council and our partners that make up the Safer Roads Partnership to develop a strategy which looks at reducing and preventing road casualties.
“In addition to undertaking enforcement and education initiatives, we need to work with local communities to ensure there are greater levels of respect by all road users, as we endeavour to make our roads safer.”