It would also significantly lengthen delivery times for those who lived some hundreds of miles from the main depot. The goods would have to travel that entire distance, including waiting for the next empty slot on a train, after they were ordered.
How does Amazon get goods to these local warehouses? If there is some kind of central distribution network then that might generate more volume on the links to the warehouses, but any trunk rail haul would probably be in containers which can be loaded onto a truck for the final leg to one of the non-rail-served terminals. With the appropriate equipment moving an ISO container from a train to a truck is always going to be quicker than transferring the same amount of stuff in roll cages one by one (even more so if they all have to go out at one end!).
Amazon has a distribution network like no other retailer, or indeed any other logistics company. Essentially there are three layers of logistics for ‘normal’ Amazon, and then a whole seperate chain for Amazon Prime. Interestingly, the logistics set up that was devised for Amazon U.K. was shown to be more efficient than the rest of Amazon’s set up and has now been replicated worldwide.
Inbound stuff for most products from suppliers to one receivable ‘Cross Dock’ centre near Coventry. This then sorts the inventory to be sent to around 15 of the 30 or so fulfilment centres (where the individual items are picked for delivery) nationwide. Many of the inbound goods will arrive in containers from the nearby rail connected logistics centres.
There’s broadly three types of fulfilment centre - one for ‘small sortable’ goods like books and stuff that fits into a small parcel less than 45cm long, one for ‘small and light’ which is bigger household stuff, and the third is ‘non sortable’ for bigger things like furniture etc.
In addition, there are some of the fulfilment centres are specialist goods - there’s one in Rugby that just does beer wine and spirits for example, one in Wales that just does shoes and clothes; these are for nationwide delivery. These specialist centres will usually receive inbound goods direct. Many of the fulfilment centres will also receive some items direct from suppliers.
Products leave the fulfilment centres to go to one of around 60 delivery stations for end delivery, where the packages are sorted down to delivery rounds for the people in white vans (other colours are available). As mentioned above, some of the fulfilment centres will distribute to delivery stations nationwide, some will distribute to delivery stations within a given region.
Prime has a different set up, with (I think) the (seperate) delivery stations each stocking a (comparatively) small range of the most popular products. This is to enable same day delivery.
The only regular bulk hauls will be from the Receiving cross dock centre in Coventry to the Fulfillment centres it serves. Even then, I’d be surprised if there were more than 15-20 wagons from Coventry to any one F.C. daily, and they will of course be spread through the day because of dock space, warehouse capacity and the number of people needed to deal with it. (Notably, the Coventry centre is over 2 miles from the nearest railway, with a lot of houses in between). The loads from each F.C. to the delivery centres will be too infrequent, variable in timing and load, and much too time critical to be considered for rail.
Apparently the next stage of the logistics network development is to link the various European networks with air freight. This is done in the US - Amazon is the only retailer with sufficient scale to have its own operation of this nature, when it rivals FedEx and UPS.
For those with an interest in logistics, it is a fascinating operation.