Speed/Distance. A horse drawn carriage typically travels about four miles per hour in traffic, so plan accordingly. Best case scenario: choose a marriage site and reception venue that are located at the same place or no more than a mile or two apart from each other. If this is not the case, be sure to allow enough travel time between the two sites. To help speed things up a bit, travel by car to meet the horse and carriage a short distance from the reception. Here you can climb aboard the carriage and still make a grand entrance in plenty of time.
Weather. While weather forecasts are helpful, they are not always 100% accurate. Be prepared for inclement weather by selecting an enclosed carriage or an open one that can easily be converted to a covered one. Have an alternative transportation plan in place, just in case (think torrential downpours, unexpected gale winds, record-breaking temperatures).
Allergies. Some people are allergic to horses. If you and your beloved have never been around a horse before, it would be a good idea to spend some time with one before the wedding. It would be a shame to have one of you sneezing, sniffling and itching your way through the nuptials.