Hewson Planning 35 Corbett Road RD2 Whangarei 082. Attachment 5. Traffic Assessment

Transcription

1 Hewson Planning 35 Corbett Road RD2 Whangarei 082 Attachment 5. Traffic Assessment 1

2 Engineering Outcomes, Limited 132 Beach Road PO Box 3048, Onerahi Whangarei New Zealand Telephone Mobile PROPOSED SUBDIVISION 561 STATE HIGHWAY 1, KAURI ASSESSMENT OF TRAFFIC EFFECTS Prepared by Dean Scanlen Engineering Outcomes Ltd

3 Table of Contents 1. INTRODUCTION DESCRIPTION OF THE PROPOSAL AND ENVIRONMENT TRAFFIC TRAFFIC GENERATION AND EXISTING TRAFFIC TRAFFIC ON EXISTING ROADS CRASHES ASSESSMENT OF TRAFFIC EFFECTS AND PROPOSED MITIGATION MEASURES... 4

4 1. INTRODUCTION This is an assessment of traffic effects of a proposed subdivision at 561 SH 1, Kauri, Whangarei including mitigation measures. 2. DESCRIPTION OF THE PROPOSAL AND ENVIRONMENT The proposal is to create three development lots from the existing one lot an increase of two lots. All lots are proposed to lead onto an existing entrance on the western side of SH 1, 60 metres north of the existing entrance to the Kauri dairy factory. In this locality, SH 1 is sealed and kerbed with three lanes (two southbound, one northbound) and a speed limit of 100 kilometres per hour. There is no existing local widening for the subdivision entrance, but extensive widening for the dairy factory entrance - a right-turn bay and left-turn lanes for both acceleration and deceleration. The entrance is beyond the exit taper for the dairy factory right-turn lane. The left-turn deceleration lane overlaps the entrance but is on the opposite side of the highway and also separated from the through lanes on the highway by a painted median. The acceleration lane is well clear of the entrance. The entrance is currently more than 12 metres wide because it leads to two other driveways, both of which lead directly onto the State highway through the entrance. The entrance is currently uncontrolled. A landscaping contracting business operates out of the parent lot and this is proposed to continue (no retail sales are involved). The entrance also leads to two rural-residential blocks and a vet practice with four staff, about 70% of the business of which is conducted off the site. There is a large orchard on the lot from which the vet practice operates. All existing lots in the catchment are developed, so there is unlikely to be potential for significant further development as permitted activities. Sight distances from the entrance are more than 250 metres in both directions. Page 1

5 Photo 1. Looking north along SH 1 from the existing and proposed entrance. Photo 2. Looking south along SH 1 from the existing and proposed entrance. Page 2

6 Photo 3. The entrance from the opposite side of SH 1. The subdivision access is to the left of the pole. 3. TRAFFIC 3.1 Traffic Generation and Existing traffic All vehicle movements are one-way, whether an entry or exit or movement in one direction along public roads. Existing traffic through the entrance is estimated as follows: Landscaping business and residence on the parent lot: 25 movements; Vet, orchard and residence: movements based on 15 daily visits from customers, the remainder by staff and in relation to the residence; From the other rural-residential lots: 20 movements. For a total of, say, 100 movements per day. The proposal is expected to increase the traffic through the entrance by twenty (20) movements per day. A high proportion of the traffic will be business related, so as much as 12% is expected in the peak hour. A high proportion is expected to travel to and from the south (including Whangarei) in the range 70 to 80%. Page 3

7 3.2 Traffic on Existing Roads The traffic on this section of SH 1 is currently 10,400 movements per day. The trend since 2004 has been a decline in the level of traffic in the order of 150 movements per day per annum 1. The 85 percentile operating speed of northbound traffic, as it approaches the site, has been measured at 97 kilometres per hour. 3.3 Crashes The Crash Analysis System (CAS) has been searched for crashes both at the existing entrance, on Richards Road (which is 400 metres to the north and on the same side of SH 1) and for 100 metres in both directions from both locations. The only reported turning crashes in this vicinity involved right turns off SH 1 onto the other side of SH 1. One of those involved a vehicle waiting in the dairy factory turning bay. 4. ASSESSMENT OF TRAFFIC EFFECTS AND PROPOSED MITIGATION MEASURES The key traffic issue with the proposal is the absence of facilities to separate vehicles turning left into the site from those not turning, and potential difficulties turning right out of the site. Even though the proposal will only increase traffic by an estimated 20%, it is proposed to address left turns into the site by installing a turning lane. In accordance with the recommendations of the Manual of Traffic Signs and Markings Part II, ( MOTSAM II ) for a 100 kilometre per hour operating speed and the maximum recommended deceleration rate of 3.5 metres/sec/sec, this lane is proposed to be a total of 110 metres long including tapers 2. The use of this deceleration rate is considered appropriate for this entrance given the relatively low level of turning traffic and the fact that the design operating speed on the northbound approach is slightly less than 100 kilometre per hour. A width of 2.5 metres outside the 3.5 metre through-lane is considered adequate because the lane will be used by very few trucks. On this basis, applying MOTSAM II, the taper would be 50 metres long. It is noted that there is currently a 4.5 metre width of carriageway between the western edge of the existing dairy factory right-turn bay and the western edge of the SH 1 seal. As such, 1.5 metres of widening is proposed in that locality. 1 Calculated from count data on the NZ Transport Agency website at count station 01N00254, which is about 250m north of north arm of Salesyards Rd. This places it 340 metres south of the subdivision entrance. The trend has been calculated using least-squares linear regression. 2 MOTSAM II refers to AUSTOADS Guide to Road Design Part 4a. The proposed deceleration distance and lane length is derived from Table 5.2 of that publication. Page 4

8 Furthermore, because of the relatively infrequent use of the entrance and its use only by cars, it is not considered necessary to install a central island or exit taper (to the left of the entrance) (all as shown in 3.20 of MOTSAM II). As such, none of those components is recommended. The proposed widening is shown in Figure 1, which is a scan of the relevant diagram from MOTSAM II amended to show what is proposed here. Page 5

9 The existing peak hour rate of both right-turn departures and left-turn entries is estimated to be between 6 and 7 movements per hour. The subdivision is expected to increase this to between 7 and 8 movements per hour. With 10% of daily traffic on the highway at this time, gap acceptance of 4 seconds and followup headway of 7 seconds, the following delays are expected for drivers departing the entrance to the right 3 : Before subdivision: 15.1 seconds; After subdivision: 15.2 seconds. This minimal effect reflects the low level of traffic on the entrance, even after subdivision. Because of this, the delays are dominated by the, much higher, level of traffic on the highway. For example, with an average of only 1.0 right-turn departure per hour, the average delay would still be 14.6 seconds. To confirm that this assessment of delays reflects the reality at the site, a survey has been carried out of actual delays at Richards Road intersection. The survey was carried out over a time period of 47 minutes between 8 and 9am on a weekday morning when schools were open. Richards Road is a no-exit public road leading to a rural-residential area that includes twelve houses and a number of businesses including a retail operation (usually unstaffed), contractor s depot and a large horticultural polyhouse operation. At the location of Richard Road s intersection, SH 1 has the same three lanes as the site entrance but is completely clear of the auxiliary lanes for the dairy factory entrance. Richards Road was chosen over the entrance itself because it was considered likely to facilitate a bigger sample. Indeed, the traffic generation from the catchment of Richards Road is likely to be 30 50% greater than that of the entrance to the subject site before subdivision, depending on the nature of the businesses in the catchment. Five right-turn exits were observed. Their waiting times averaged 18 seconds and ranged from 7 to 40 seconds. Only one queue was observed. It consisted of two vehicles for a period of less than 5 seconds. While this delay is slightly longer than indicated by the theory, it is well within the margin of error given the necessarily small sample. It is also noted that the southbound passing lane on SH 1 will often be useful as an acceleration lane from the site. Given the excellent visibility, this is likely to be desirable in minimising any delays to existing vehicles from vehicles turning right from the subdivision entrance. In fact, almost all delays will be experienced only by the drivers of the turning vehicles, not those on the highway. The effect on existing users of the access will be so small as not to be noticeable. These turns, and their associated delays, have not resulted in any reported crashes in a 5-year period on either the entrance or on Richards Road. 3 Using accepted formulae for delays at intersections and entrances that experience random traffic, with accepted parameters for drivers making right-turn departures. This is as reproduced in AUSTROADS Guide to Road Design Parts 4 Intersections and Crossings. Traffic is random when sufficient isolated from traffic signals as this site it. Page 6

10 With the proposed left-turn deceleration lane and the separation between the SH 1 through lanes and dairy factory left-turn lane, the proximity of the entrance to the dairy factory entrance is considered to have negligible effect. In particular, the width of the deceleration lane will be more than adequate for a northbound, nonturning vehicle to move between two other decelerating vehicles (one turning right into the dairy factory, the other turning left into the site), even a truck. In any event, the coincidence of two vehicles decelerating in this way will be extremely rare. In fact, with the relatively small proportional increase in traffic as a result of the subdivision, the left turn lane is considered to provide an overall positive effect (benefit). Safe Intersection Sight Distance is exceeded in both directions along all sightline vectors. That is the highest standard applicable for considerations of safety. As a result, the entrance will have an adequate factor of safety in relation to exits. Overall, with the proposed left turn lane, it is concluded that the traffic effects of the proposal will be well within acceptable limits and that there are no traffic-related impediments to the granting of consent. Dean Scanlen BE(Hons)(Civil), CPEng, IntPE(NZ) Page 7