Algorithm 1. Method of Relay-Node Selection on Curved Roads
1	Input: Set of Nodes $\mathrm{N}$, Obstacles ${\rm O}$.
2	Input: Message sender $S$, previous sender $S_{\mathrm{pre}}$, terminal point $P_{\mathrm{end}}$.
3	Output: Relay-node on curved roads.
4	Phase 1. Judgment Phase:
5	if there is an area between $S$ and $S_{\mathrm{pre}}$ that is blocked by ${\rm O}$ or out of the communication range of $S$ and $S_{\mathrm{pre}}$.
6	Determine the area as a vacant.
7	Phase 2. RTB Packet Broadcast Phase:
8	if there is a vacant between $S$ and $S_{\mathrm{pre}}$
9	Set the mode flag of RTB packet to 3 (means simultaneously start the normal selection and the reverse selection).
10	Determine the optimal position $P_{\mathrm{opt}\_\mathrm{norm}}$ in the message propagation direction according to Definition 1.
11	Choose the nearest corner as the optimal position $P_{\mathrm{opt}\_\mathrm{rev}}$ in the reverse direction.
12	Determine the endpoint of the vacant closest to $S_{\mathrm{pre}}$ as the termination of the reverse selection $P_{\mathrm{rev}\_\mathrm{end}}$.
13	Add $P_{\mathrm{opt}\_\mathrm{norm}}$, $P_{\mathrm{opt}\_\mathrm{rev}}$, $P_{\mathrm{rev}\_\mathrm{end}}$ into the RTB packet.
14	else if be on the road between $S$ and $S_{\mathrm{pre}}$.
15	Set the mode flag of RTB packet to 2 (means start the reverse selection).
16	Choose the next corner as the optimal position $P_{\mathrm{opt}\_\mathrm{rev}}$ in the reverse direction
17	Update $P_{\mathrm{opt}\_\mathrm{rev}}$ in the RTB packet.
18	Else
19	Set the mode flag of RTB packet to 1 (means start the normal selection).
20	Determine the optimal position $P_{\mathrm{opt}\_\mathrm{norm}}$ in the message propagation direction according to Definition 1.
21	Update $P_{\mathrm{opt}\_\mathrm{norm}}$ in the RTB packet.
22	Broadcast the RTB packet.
23	Phase 3. Relay-Node Selection Phase:
24	if the mode flag of RTB packet is 3
25	Start EPBP with $P_{\mathrm{opt}\_\mathrm{norm}}$ as the optimal position, $n_{\mathrm{norm}}\in \mathrm{N}$ is not blocked by ${\rm O}$ is selected as the relay-node in the message propagation direction.
26	Simultaneously, start EPBP with $P_{\mathrm{opt}\_\mathrm{rev}}$ as the optimal position, and $n_{\mathrm{rever}}\in \mathrm{N}$ is not blocked by ${\rm O}$ is selected as the relay-node in the reverse direction.
27	else if the mode flag of RTB packet is 2
28	Start EPBP with $P_{\mathrm{opt}\_\mathrm{rev}}$ as the optimal position.
29	$n_{\mathrm{rever}}\in \mathrm{N}$ is not blocked by ${\rm O}$ is selected as the relay-node.
30	Else
31	Start EPBP with $P_{\mathrm{opt}\_\mathrm{norm}}$ as the optimal position.
32	$n_{\mathrm{norm}}\in \mathrm{N}$ is not blocked by ${\rm O}$ is selected as the relay-node.
33	Relay-node selection finished