The speed limit policy in New Zealand is a national policy that aims to balance mobility and safety by setting speed limits that are safe, appropriate, and credible for the level of roadside development and the category of road.

The information required to determine the speed limit for a particular road is: The existing speed limit;

• The character of the surrounding land environment (e.g., rural, fringe of city, fully developed);
• The function of a road (i.e., arterial, collector or local);
• Detailed roadside development data (e.g., number of houses, shops, schools, etc.);
• The number and nature of side roads;
• Carriageway characteristics (e.g., median divided, lane width and number of lanes, road geometry, street lighting, footpaths, cycle lanes, parking, setback of fence line from carriageway);
• Vehicle, cycle and pedestrian activity;
• Crash data; and
• Speed survey data.

Calculating a speed limit using Speed Limits New Zealand (SLNZ) methods requires road and roadside data collection, and the application of the set procedures specified in the policy.

Once a section of road has been identified for analysis, data collection should be commenced. The survey should extend at least 200 meters in each direction beyond the section of road under consideration. This is to ensure the appropriate boundary point between speed limits is identified and features that may influence sign location are included.

Step 1: Determine Development Rating

Different types of development are allocated for the rating values as shown in Table SLNZ4. The ratings are based on the expected number of vehicle, pedestrian and cycle movements generated each day. For example, a house is allocated one rating unit and a large shop is given four rating units.

Development ratings are allocated for the road being surveyed (frontage development) and for the first 500 meters of side roads (side road development). For each 100-meter section of road, the development rating subtotal is the sum of the frontage and the side road development ratings. The total development rating is calculated by adding the 100-meter subtotals for the length of road being assessed for a speed limit.

Table E1. Development Rating

* An access point includes a private driveway and a public entrance or exit.
** A dwelling includes a house, a home unit in a block, a semi-detached home unit, and a motel unit. Each unit in a block of units counts as one dwelling.
*** When two or more developments other than dwellings, or if dwellings and other developments share a common access point or service road, the correct rating is the greatest of:

• • the rating for a development type A, B, or C according to the number of dwellings served by the access point; or
• • the highest rating for any one development, other than dwellings, served by the access point; or
• • the rating determined by treating the access point as a side road and allocating the rating specified in Table SLNZ5.

Multiple access points are handled in the following manner:

• Where a single development or a small group of developments has more than one access point on the same road, the development should be rated once only and additional access points ignored. Developments with separate entrance and exit points should also be treated as having only one access point. Examples include service stations, motels, schools, and a small group of shops with off-street parking.
• Where a large group of developments, such as a shopping mall or a service road, share more than one access point, a rating is assigned to each access point. In these situations, a proportional number of the developments should be allocated to each access point, and each one rated as a Development Type E.
• Separate ratings may be assigned to each access point when there are at least four individual developments or one type D development for each access point. These conditions ensure that the sum of the access point ratings does not exceed the sum of the ratings for the individual developments in the group.

Step 2: Determine side road development rating

The side road development rating is calculated on the first 500 meters of a side road by applying the rating values outlined in Table E1 to the development and then entering Table E2 to determine the side road rating.

A notable difference in this step is that each school or kindergarten fronting on a side road is calculated (differently) as follows:

• Use half the normal frontage rating (from Table E1) if a school or kindergarten is within 500 meters from the road being surveyed; and
• Use a quarter of the frontage rating (from Table E1) if a school or kindergarten is between 500 and 1000 meters from the road being surveyed.

Note that a cross intersection is treated as two side roads.

Table E2. Side Road Development Rating

Step 3: Roadway Rating

The roadway rating is calculated by summing the ratings related to roadway activities and traffic control. Tables E3 to E8 show the ratings that apply according to the nature and use of the road. Note that where usage or provision of facilities is different on each side of the road, the rating is the average of the ratings for each side.

Roadway ratings are calculated for each 100-meter section of road and the sub-total is the sum of the ratings for each roadway activity per 100-meter section. The total roadway rating is calculated by adding the 100-meter sub-totals for the length of road being assessed for a speed limit.

Step 4: Calculate the Rating

The average rating is calculated by summing the total development and roadway rating for the length of road being assessed and then dividing by the number of 100-meter sections of road. However,

the total roadway rating must not exceed the total development rating for the length of road being assessed. If the total roadway rating is higher, it must be reduced to that of the development rating.

Table E3. Pedestrians

Table E4. Cyclists

Table E5. Parking

Table E6. Road Geometry

Table E7. Traffic Control

Table E8. Development

Step 5: Determine the Speed Limit

When the average rating has been calculated, the speed limit is determined as follows.

(Extended Text Description: Figure SLNZ1. Determining Speed Limit. At the top left there is a label entitled "Surrounding land environment" and on the top right there is a label entitled "Location". Under the "Surrounding land environment" label is the following text, from top to bottom: "Fully rural," "Rural selling placem," and "Settlements", each with arrows pointing to a box under "Location" entitled "Rural (See Fig. SLNZ2)". Under "Settlements" on the left, there is text which reads "Fringe of city or town" with an arrow pointing to a box under the prior "Rural" box, labeled, "In-between (See Fig. SLNZ3)". Under "Fringe of city or town" on the left, there is text which reads, "Low density development" and "Full developed," each with arrows pointing to a box under the prior "In-between", labeled, "Urban (See Fig. SLNZ4)".)

Figure SLNZ1. Determining Speed Limit.

(Extended Text Description: Figure SLNZ2. Speed Limit Flow Chart—Rural. The flow chart starts on the left with a circle which reads "Rural", which has four arrows pointing to a vertical column of four boxes entitled "Average rating (R)." On the right is a veritcal column of four circles with numbers entitled "Speed limit". The first of the four boxes on the left says "R >= 11" with an arrow that point to a box on the right labeled "Note 1" which has another arrow to the right to a circle with the number "50" in it in the "Speed limit" column of circles. The second of the four boxes says "11 > R >= 6" with an arrow leading to speed limit circle of "70". The third box says "6 > R >= 3" with an arrow leading to a speed limit circle of "80". The fourth and final box says "R < 3" with an arrow leading to a speed limit circle of "100". At the bottom of the flow chart is the following note: "Note 1. The level of development is not consistent with the location of this road. Please check you have used the correct flow chart for the location (see Fig. SLNZ1).)

Figure SLNZ2. Speed Limit Flow Chart—Rural.

(Extended Text Description: Figure SLNZ3. Speed Limit Flow Chart—In-Between. This flow cart begins on the upper left with a circled labeled "In-between" with arrows leading to a circle labeled "Arterial" and another circle labeled "Local/collector". The "Arterial" circle leads to four boxes in a vertical "Average rating (R)" column. The first box is "R>=11", the second box is "11 > R >= 6", the third box is "6 > R >= 3" and the fourth box is "R < 3". The circle labeled "Local/collector" points to four boxes as well, underneath the first four boxes in the "Average rating (R)" column. The first box in this second set of boxes is "R>=11", the second box is "11 > R >= 6", the third box is "6 > R >= 3" and the fourth box is "R < 3". The first box labeled "R>=11" at the top of the "Average rating (R)" column points to a larger vertical box with the following text: "Does the road have all of the following characteristics: A median >= 4.5m or a fully protected media? Lanes >= 3.5m? Setback >= 6m? Route lighting? Mean operating speed >= 60km/h? 85th %ile speed >=70km/h?" This large box has a bracket to the right with the following text: "No to any" points to a circle "50" speed limit, "Yes to all" points to a circle "60" speed limit. The "11 > R >= 6" box points to a circle "70" speed limit. The "6 > R >=3" box points to a circle "80" speed limit. The "R < 3" box points to a circle "100" speed limit. Finally, the bottom four boxes in the "Average rating (R)" point as follows: The "R >= 11" box points to a circle "50" speed limit. The "11 > R >= 6" box points to a circle "70" speed limit. The "6 > R >=3" box points to a circle "80" speed limit. The "R < 3" box points to a circle "100" speed limit. )

Figure SLNZ3. Speed Limit Flow Chart—In-Between.

(Extended Text Description: Figure SLNZ4. Speed Limit Flow Chart—Urban. This flow cart begins on the upper left with a circled labeled "Urban" with arrows leading to a circle labeled "Arterial" and another circle labeled "Local/collector". The "Arterial" circle leads to four boxes in a vertical "Average rating (R)" column. The first box is "R>=11", the second box is "11 > R >= 6", the third box is "6 > R >= 3" and the fourth box is "R < 3". The circle labeled "Local/collector" points to four boxes as well, underneath the first four boxes in the "Average rating (R)" column. The first box in this second set of boxes is "R>=11", the second box is "11 > R >= 6", the third box is "6 > R >= 3" and the fourth box is "R < 3". The first box labeled "R>=11" at the top of the "Average rating (R)" column points to a larger vertical box with the following text: "Does the road have all of the following characteristics: A median >= 4.5m or a fully protected media? Lanes >= 3.5m? Setback >= 6m? Route lighting? Mean operating speed >= 60km/h? 85th %ile speed >=70km/h?" This large box has a bracket to the right with the following text: "No to any" points to a circle "50" speed limit, "Yes to all" points to a circle "60" speed limit. The "11 > R >= 6" box points to a circle "70" speed limit. The "6 > R >=3" box points to a circle "80" speed limit. The "R < 3" box points to another box labeled "Note 1". Finally, the bottom four boxes in the "Average rating (R)" point as follows: The "R >= 11" box points to a box labeled "With engineering to control speed", which points to circles "20", "30", and "40" speed limits, while also pointing directly to "50" speed limit. The "11 > R >= 6" box points to a circle "70" speed limit. The "6 > R >=3" box points to a circle "80" speed limit. The "R < 3" box points to a box labeled "Note 1" which then points to a circle "100" speed limit.)

Figure SLNZ4. Speed Limit Flow Chart—Urban.

In rare instances, because of special features or activities along a road, SLNZ cannot be used or will not produce a sound result. SLNZ must always be used with reference to speed limits policy, and in conjunction with sound engineering judgment, to determine the appropriate and safe speed limit.