Sussex Police is appealing for information about the crash which happened near Angmering on Friday.
Local authorities have acknowledged the issue and say they are committed to improving conditions.
Southern Railway calls the incident at Angmering train station "reckless and extremely dangerous".
Charlie is fundraising to allow as many people as possible to receive the same treatment as him.
National Highways described the crash on the A27 westbound at Angmering as "serious".
A campaign group is fighting to prevent developers from building 190 homes in Angmering.
The A259 was closed in both directions while fertiliser was cleared from the scene.
