Compared to other types of intersections, roundabouts have demonstrated multiple benefits such as improved traffic safety, pedestrian safety, and road capacity, as well as reduced congestion, pollution, and energy consumption [
1,
2]. Compact roundabouts also have traffic calming effects by reducing vehicle speeds using geometric design elements [
3]. However, driving through a roundabout involves a more complicated decision-making process. Moreover, roundabouts in China are often constructed at large intersections. The complex environment in a large roundabout does not provide essential directional information to motorists. In other words, drivers must spend more time identifying the exit they want, which may decrease the operational efficiency of roundabouts. In order to improve sense of direction, a simple and low-cost method was proposed in this paper using traffic signs and pavement markings rather than relying only on road reconstruction.
Traffic signs and road markings provide essential information to road users, which guide motorists and regulate their driving behaviors [
4]. With the installment of traffic signs and road markings, road traffic operates with safety, convenience, and efficiency. Countries all over the world have largely agreed on the principles for the design (shape, color, size, and layout) of traffic signs, but different parts of the world have applied different rules, which contribute to variations on signs and markings. Many studies have examined the effects of the various dimensions of traffic signs and road markings, such as background color [
5], symbol and text mixture [
6], visibility and legibility [
7], and lighting criteria [
8]. Moreover, the number of signs and road markings [
9,
10] and location selection [
11,
12] have also been widely studied. Another large body of research has explored factors associated with the correct comprehension of traffic signs and road markings [
13,
14,
15]. Ng and Chan addressed the effects of driver factors (age, gender, driving frequency, driving experience) and sign design features (familiarity, concreteness, simplicity, meaningfulness, semantic closeness) on the comprehensibility of traffic signs, finding that motorists were able to better understand the meaning of traffic signs which were familiar, simple, meaningful, and associated with underlying concepts [
16,
17]. Generally, too much information provided by traffic signs and road markings may increase driver’s visual load and negatively affect driving performance [
18,
19]. Too little information may also be a problem, as drivers need more time to make decisions in a complex driving environment and must rely more on their own driving experience [
20]. Overall, existing literature focused more on the effects of stand-alone traffic signs and road markings rather than components of an integrated system.
When driving through a roundabout, the surrounding environment will rotate to a certain extent in the driver’s view and the rotation of visual cues will vary with the change of viewing angles. Therefore, drivers need mental rotation ability to identify the exit they want. Mental rotation is the ability to rotate an object in one’s mind and is an essential paradigm for spatial ability. Shepard and Metzler first introduced the concept of mental rotation in a remarkably elegant experiment in which participants were presented with two images of cubes and asked to determine whether the right image was a rotation or mirror of the left [
21]. The experimental results clearly supported that participants’ reaction time increased linearly as the angular difference between the two cubes increased. There is evidence indicating that gender and age differences exist in mental rotation abilities. Males and younger adults typically outperform females and older adults on spatial perception tasks [
22]. Although human mental rotation ability has a certain capacity [
23], mental rotation performance can be improved by training which focuses on practicing with spatial tasks and materials. Attentive visual references can also contribute to the improvement of mental rotation abilities [
24,
25].
Perceptual constancy is a phenomenon in which an object is seen in the same way under varying circumstances [
26]. For example, color constancy is a form of perceptual constancy which ensures that the perceived color of an object remains similar under varying illumination conditions. Similarly, shape constancy is the tendency to perceive an object as having a relatively constant shape regardless of its orientation or the viewing angle. Moreover, color and shape are dominant visual features of traffic signs and road markings and can provide key information that drivers need to process when driving along the road [
27]. Therefore, color constancy and shape constancy can be used to mitigate the rotation of visual cues under varying conditions and improve the driver’s mental rotation ability and sense of direction.
Installing guide signs and pavement markings is a simple and low-cost solution that can reduce visual load and improve sense of direction. Considering color constancy and shape constancy, a continuous and gradual guide sign system was proposed to improve the safety and efficiency of roundabout operations. Then, a driving simulator was used to quantitatively analyze the effect of this guide sign system on drivers’ mental rotation ability. The guide sign system proposed in this paper is expected to provide a reference guide for the effective design of guide sign in complex roundabouts.