Here they had stopped maintaining 175, 400, and 1000W mercs around 2000. They kept relamping 100W mercs for whatever reason (I think because there were so many of them left when NGrid bought out NECo in 2000) until around 2014. Now they replace all mercs with HPS upon needing service. No LEDs on utility poles here, though RIDOT is installing some LEDs. RIDOT still relamps existing HPS fixtures and spot replaces with an equal light. If it's a drop lens HPS, it gets replaced with a drop lens HPS if it fails and if it's an FCO HPS it gets replaced with an FCO HPS when it fails. They don't mix drop lens and HPS (except in very rare instances; only seen it a couple of times) and so far haven't mixed HPS and LED.
So far RIDOT has swapped out the HPS lights at all the Park-N-Ride lots with LEDs,
Exits 1 and 2 on I-95 near Connecticut (at these interchanges they replaced the NGrid-owned truss poles with their own RIDOT-owned metered davits),
Exit 7 on I-295 (just a cobrahead-to-panel swap),
Exits 6 and 7 on RI Route 4 (cobrahead-to-panel swap, keeping the RIDOT poles), the
Hartford Avenue exit on US Route 6, and the
Reservoir Ave exit on RI Rte 10, where you can see the new poles were up but the old poles were not yet removed. FYI, those trusses on Route 10 originally held GE Form 400 Powerpacks! The truss poles were all owned by National Grid (then it was Narragansett Electric Company before NGrid bought them out). The lights are "rented" by the state DOT just like wood pole lights are "rented" to the city. I don't think the metal poles lights are charged the same way wood pole lights are though. The metal poles are unmetered but I don't think it's a per-light charge. At any rate, RIDOT is eventually going to replace all the remaining NGrid-owned lights with their own RIDOT-owned poles, which will be metered. That way RIDOT will only get charged for usage and they can program the relay cabinets to shut the lights off in the middle of the night. The NGrid poles have photocells and run dusk-to-dawn (that is, when there aren't wiring issues; NGrid is horrible at maintaining the freeway lights).