Replace the carriages with sedan chairs, and the horses with homeless people? 
Is there a “greener” form of transportation than a horse and carriage?
bicycle
forcing the peons to walk?
rickshaw?
From what I've seen, horses don't fully burn all of the hay they consume.
An interesting footnote to the whole fandango is that New York City owes its fine robust water supply to horse drawn carriages. The water supply system and storm drains were designed to allow for daily (early AM) sweeping of every street in Manhattan, followed by a wash down from fire hydrants. As the horses disappeared, early in the 20th Century, the practice was discontinued. Around 1985, they made the horses start wearing diapers! My wife always wanted a ride in a Hansom carriage. Last summer we stopped in Freeport, ME for some sort of L.L. Bean promotion. Attendant thereto, you could get a ride around downtown in a horse drawn carriage for $20 bucks, so we did it, starting at the L.L. Bean main store. It was fun.
Replace the carriages with sedan chairs, and the horses with homeless people?
Envior Problems:
An average horse will produce 20.4 kilos (or 45 pounds) of manure each day, equating to 7.5 tonnes annually! This quantity does not include the addition of soiled stable bedding material. Whilst some manure is dropped onto fields when horses and ponies are turned out, best practice usually involves the collection and removal of droppings from pasture. This assists paddock hygiene (minimising parasite burdens), maximises the grazing potential available from pasture by preventing latrine areas and improves the appearance of the holding.
Then, the gallon plus of urine each day can add to enviral problems.
Daily horse flatus will add to enviral problems.
Yes. A man on a bicycle.
Was thinking the same thing. Horse and carriage is "greener" than electric car.