Grouping Datetimes to Identify Sessions

Let's say that I have a record of events that are unique by a datetime "timestamp" marker, and that these events can be grouped by sessions, so that every event that occurs within a certain period of time of the preceeding and/or subsequent events to it are considered as part of the same session. For example, let's say that we are examining cars driving by a traffic counter where each car passing is recorded as an event, and we want to organize the events by sessions so that any two cars passing within 5 seconds of one another constitutes a session (the events will "chain" together so that if four cars pass within 2 seconds of one another, but the first and last cars are within 10 seconds, all four car events are a part of the same session).

Now, if I only have the events, how do I create sessions around them?