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My TomTom Sat Nav usefully prompts you with the speed limit for the road you are driving on, and although they have a disclaimer saying that the accuracy for being up-to-date cannot be guaranteed, I have noticed that all UK motorway and dual-carriageway slip roads and any interconnecting roads, whether they are single or dual-carriageways, are indicated to be 60mph.

I would have thought that the speed limit for slip roads and interconnecting dual-carriageways (e.g. road connecting M3 to M27) would be the same as the speed limit for the motorway, which in the case of cars, motorcycles, car-derived vans and dual-purpose vehicles, is 70mph (when not towing a trailer, other vehicle or caravan).

I have always believed that The Highway Code is the go to for the laws regarding driving within the UK, yet the page on Speed Limits does not answer the question.

What is the situation within the UK?

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    British-to-American dictionary, in case it helps anyone: "slip road" = "on/off ramp". – David Richerby Dec 15 '18 at 8:45
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    Perhaps due to the uncertainty TomTom is being "safe", that is, not over-rating it. However, if the limit is 60 that would make it impossible to legally match your speed to vehicles on the motorway doing 70 mph, which is unsafe. – Weather Vane Dec 15 '18 at 8:58
  • I would have thought (and expect) the speed limit will be whatever shown on the sign at the start of the slip road. Usually they will be the national speed limit, but having lived in London for such a long time, I know for sure that is not a granted. Will expand that as an answer. – B.Liu Dec 15 '18 at 9:11
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    @B.Liu If the road you approach the slip road from is already at the national speed limit, there is no sign on the slip road. – Weather Vane Dec 15 '18 at 9:14
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    I've wondered about this, especially with regard to the limit on the roundabout at J9 of the M23. The roundabout itself is part of the M23 (somewhat unusually, I was assured by the copper who picked me up for hitchhiking on the motorway some number of years ago and dropped me off at Gatwick station), and there doesn't appear to be any speed restrictions. – spender Dec 15 '18 at 19:05
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On entering the M11 southbound slip road from a roundabout on the B184, there is immediately a pair of blue signs saying M11. According to the Highway Code they indicate the "start of motorway and point from which motorway regulations apply". Since you are now on a motorway and there is no other speed restriction, the limit for cars etc from this point is 70mph as shown in your Highway Code reference.

cropped

Image from Google street view.

Similarly on leaving the M11 at J10 northbound, the "End of Motorway" sign is at the far end of the slip road, just before the roundabout at the A505.

enter image description here

Image from Google street view.

Also the interconnecting roads between motorways do not have any "End of Motorway" signs.

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  • All motorway slip roads are part of the motorway. This is from the last point you can avoid entering the motorway, to the first point that you can join another road. – CSM Dec 15 '18 at 14:37
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Short summary: There is not a universal speed limit on UK slip roads. While in general the national speed limit for motorway applies, if there is a speed limit sign stating otherwise you should follow that instead.

According to [Highway Code Rule 124](https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158）:

Rule 124

You MUST NOT exceed the maximum speed limits for the road and for your vehicle (see the speed limits table).

This means in general, the motorway national speed limit applies on slip roads (given it under motorway restrictions, see @Weather Vane's answer). However if there is a speed sign installed that indicates otherwise, that would be the actual speed limit.

The actual speed limit on a motorway then could be:

  • The national speed limit, whether it be:

    • A new speed limit sign (e.g. The speed limit sign on a slip road from A720 on to M8 (J1), curiously it is showing 70mph instead of the national speed limit);
    • A sign saying it is a motorway, and hence motorway restrictions (see Highway code 253-273) apply, at the beginning at the slip road; or
    • A lack of sign when you join from a road already having a national speed limit (e.g. All 4 slip roads between the M3/M27 Junction, though advisory speed limit is sometimes in force according to Google Maps).*

  • The speed limit of the motorway you are joining (e.g. this slip road joining M32 in Bristol has a speed limit of 40mph, that on that particular stretch in M32.

Or, in fact:

A 40mph limit specified by the variable speed limit indicator in M4 J4B Westbound

Somewhere else in Birmingham, a 30mph limit is (was?) imposed temporary on a slip road on the Spaghetti Junction due to works (A38(M) Northbound J6, leading to M6 Eastbound, Image also from Google Maps):

A 30mph limit is imposed temporary on a slip road on the Spaghetti Junction due to works

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    The presumed speed limit is 30 MPH when you are in a built up area (with street lamps) – Douglas Held Dec 15 '18 at 11:46
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    @B.Liu The quote at the top of the government page is misleading. It only applies to roads with street lights, not to all roads. Only about 30% of the UK "strategic road network" (including motorways) has ever had lighting. – alephzero Dec 15 '18 at 14:41
  • Now I have reread the comments and the highway code (rule 124/125), I can see where the confusion is coming from. While I intended for the answer to be "read the signs, if not assume national speed limit", the quote clearly steers readers away from that direction. I will try to fix the text now. Thank you for all your comments. – B.Liu Dec 15 '18 at 15:40

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