In A Duke in Shining Armor, my characters travel, at one point, in a post chaise.
At the Jane Austen Society of North America, you can read Ed Ratcliffe’s carefully researched and detailed paper on transport in the early 1800s. If you scroll down about a third of the way you’ll come to the post chaise part. On her website, Candice Hern covers the topic rather more briefly.
And/or you can read my, also brief, version:
A post chaise was usually a hired vehicle, rather like a long-distance taxi-cab. They were not driven by a coachmen but by postilions or postboys (they were “boys” no matter how old they were), who rode the “near” or left side horse. The vehicles tended to be small, holding two passengers in tight quarters on a single seat. This intimacy is one reason I like to have my hero and heroine travel by post chaise.
Another reason is speed. If you traveled in your own vehicle, with your own horses, you’d need to stop to water/feed and rest the horses at frequent intervals, say every six to twenty miles, depending on how slowly you travel, and road condition, e.g., level, uphill, well or poorly maintained. The rest period could take hours.
Instead, with a post chaise, at similar intervals, determined by road conditions, you stopped at a posting inn and changed for fresh horses. This change took very little time, and off you’d go again. The posting inns maintained a good supply of horses. Also, for a long journey, there would be postilions or postboys available to take over for your tired driver. About every other stop, you’d change vehicles, too, so that the owners of the operation could keep track of their property.
The photograph is from my 2009 visit to Colonial Williamsburg. Coachman Susan Billeter Cochrane stands with the horse saddled for her to ride postilion. Note that she wears a leather guard over her left boot to protect it from close contact with the other horse.