ExpressRoute now supports up to 4 circuits from a single peering location connected to an ExpressRoute virtual network gateway, which was previously limited to a single circuit in a peering location. This is generally available in Azure Public. Read the documentation here.
Customers can use secondary and ancillary connections in the same peering location to allow for connectivity from different private networks, as well as to provide redundancy via multiple service providers. See here for a list of providers in a given peering location.