Fast public transport from Kusatsu to Jigokudani Monkey Park during winter?

I have sent an email to the tourist office, and they replied:

• The direct road is not accessible by car until April the 24th. A not-so-big detour via Ueda is the best (see screenshot below).
• By public transport, the best is to take the bus from Kusatsu to Karuizawa, then the normal train from Karuizawa to Nagano and Yudanaka.

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http://www.kusatsu-onsen.ne.jp/access/train03.php

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???????????????????????train route finder "Jordan"

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http://www.jorudan.co.jp/english/

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http://www.shibuonsen.net/yaenkoen/

There is a bus that runs between the two from Shirone Kazan (????) which is right next to Kusatsu to Yudanaka (???) for 1500 yen and only takes 80 minutes (barring traffic jams). From Yudanaka you can walk to Jigokudani in about 30 minutes or so.

However this website hasn't been updated since November and it sounds like the schedule may have changed then so it may be a good idea to email the people who run this website (the Kusatsu Onsen Tourism Bureau) and ask.

If the bus isn't running and you can rent a car that is the best bet, as it will get your to Jigokudani much quicker.