A government agency which manages the A1(M) has maintained the Hertfordshire stretch of the motorway is “among the safest” despite a fatal crash on Saturday bringing the death toll to six in 16 months.

Sean Clasper, of Sittingbourne in Kent, died after his blue Toyota Celica overturned at junction 7 of the A1(M) near Stevenage at approximately 11.30am. Emergency services, including an air ambulance, were called but the 45-year-old was pronounced dead at the scene.

Mr Clasper’s two children, aged nine and 11, were hospitalised with serious injuries along with their mother. The children have since been discharged and their mother remains in a stable condition at Addenbrooke’s Hospital in Cambridge.

The incident is the second fatal crash between junctions 2-9 since the turn of the year following the death of Christopher Munsami, who died after coming off his motorbike near to the Hatfield Tunnel in February. The 24-year-old worked at Fujitsu in Stevenage as an IT technician.

Hertfordshire Constabulary recorded four deaths on the stretch of road in 2013 – a four-year high for the area. There were no fatal collisions recorded in 2012 and one each in 2010 and 2011.

Saturday’s fatal crash also comes less than 24 hours after another accident near Stevenage – at junction 8 – when a black Audi crashed on the northbound sliproad. The driver was taken to Lister Hospital with minor injuries.

Asked to respond to the rising number of fatalities on the A1(M), a spokesman for the Highways Agency, which maintains the UK road network on behalf of the Goverment’s Depart­ment for Trans­port, said: “Road safety is our top priority. The A1(M) between junctions 2-9 is a key corridor in and out of London, through Hertfordshire, but is, on average, among the safest compared to similar types of roads.”

Stevenage MP Stephen McPartland said: “The incident on Saturday is a terrible tragedy and my thoughts are with the families of those affected at the moment. Every fatality on our roads is one too many and huge amounts of money has been invested in trying to make our roads safer.

“Sadly, the money doesn’t seem to stop the problem, as it only takes a split second for a driver to lose control of their vehicle and when travelling at high speed this can lead to serious injuries and deaths. I hope this is the last fatal accident we will see on our stretch of the A1(M) for a long time.”

Ambulance officer Gary Sanderson, who works for the East of England Ambulance Service NHS Trust, said: “Over the last 12 months I have attended several road traffic collisions which resulted in serious injuries and, sadly, fatalities.

“Partnership is vital to educate the public about the dangers associated with our roads and our aim is to reduce the amount of injuries and fatalities that we see throughout the year as they are all too often.”

Police have issued a witness appeal in order to find out more about the events leading up to the crash. Officers from the Collision Investigation Unit are specifically appealing for information from anyone who saw a dark blue Toyota Celica, which was involved in the collision, and a black Ford Mondeo prior to the incident.

Anyone with information is asked to contact PC Andy Ralph via the non-emergency number 101.