A serious collision this morning has now called for an appeal for information.
Officers attended, alongside the ambulance service, and the pedestrian – a four-year-old boy – was taken to hospital with a serious injury to his abdomen.
Bus services had to divert, and disruptions to Friday’s refuse collection service were not able to do certain streets.
The road was re-opened around 3pm.
Sergeant Simon Cooper, from the Bedfordshire, Cambridgeshire and Hertfordshire Road Policing Unit, said: “We are still establishing the circumstances of this collision which has left a small child very badly injured.
“Were you in the area? Did you see what happened? Any information you have, no matter how small it might seem, could be vital to our investigation.
“I would also like to urge anyone who was in the area and has a dashcam fitted to their vehicle to please check it. You may have captured something useful so please do have a look and let me know if you think it could be of use to our investigation.
“If you can help, please call the non-emergency number 101 or email me at firstname.lastname@example.org quoting ISR 239 of 21 August.”